Posts Tagged halpha emission

Recent Postings from halpha emission

The Survey of Lines in M31 (SLIM): Investigating the Origins of [CII] Emission

The [CII] 158 micron line is one of the strongest emission lines observed in star-forming galaxies, and has been empirically measured to correlate with the star formation rate (SFR) globally and on ~kpc scales. However, due to the multi-phase origins of [CII], one might expect this relation to break down at small scales. We investigate the origins of [CII] emission by examining high spatial resolution observations of [CII] in M31, with the Survey of Lines in M31 (SLIM). We present five ~700×700 pc (3"x3") Fields mapping the [CII] emission, Halpha emission, combined with ancillary infrared (IR) data. We spatially separate star-forming regions from diffuse gas and dust emission on ~50 pc scales. We find that the [CII] – SFR correlation holds even at these scales, although the relation typically has a flatter slope than found at larger (~kpc) scales. While the Halpha emission in M31 is concentrated in the SFR regions, we find that a significant amount (~20-90%) of the [CII] emission comes from outside star-forming regions, and that the total IR (TIR) emission has the highest diffuse fraction of all SFR tracers. We find a weak correlation of the [CII]/TIR to dust color in each Field, and find a large scale trend of increasing [CII]/TIR with galactocentric radius. The differences in the relative diffuse fractions of [CII], Halpha and IR tracers are likely caused by a combination of energetic photon leakage from HII regions and heating by the diffuse radiation field arising from older (B-star) stellar populations. However, we find that by averaging our measurements over ~kpc scales, these effects are minimized, and the relation between [CII] and SFR found in other nearby galaxy studies is retrieved.

The continued optical to mid-IR evolution of V838 Monocerotis

The eruptive variable V838 Monocerotis gained notoriety in 2002 when it brightened nine magnitudes in a series of three outbursts and then rapidly evolved into an extremely cool supergiant. We present optical, near-IR, and mid-IR spectroscopic and photometric observations of V838 Monocerotis obtained between 2008 and 2012 at the Apache Point Observatory 3.5m, NASA IRTF 3m, and Gemini South 8m telescopes. We contemporaneously analyze the optical & IR spectroscopic properties of V838 Monocerotis to arrive at a revised spectral type L3 supergiant and effective temperature Teff~2000–2200 K. Because there are no existing optical observational data for L supergiants in the optical, we speculate that V838 Monocerotis may represent the prototype for L supergiants in this wavelength regime. We find a low level of Halpha emission present in the system, consistent with interaction between V838 Monocerotis and its B3V binary; however, we cannot rule out a stellar collision as the genesis event, which could result in the observed Halpha activity. Based upon a two-component blackbody fit to all wavelengths of our data, we conclude that, as of 2009, a shell of ejecta surrounded V838 Monocerotis at a radius of R=263+/-10 AU with a temperature of T=285+/-2 K. This result is consistent with IR interferometric observations from the same era and predictions from the Lynch et al. model of the expanding system, which provides a simple framework for understanding this complicated system.

Environments of interacting transients: Impostors and type IIn supernovae

This paper presents one of the first environmental analyses of the locations of the class of `interacting transients’, namely type IIn supernovae and supernova Impostors. We discuss the association of these transients with star formation, host galaxy type, metallicity, and the locations of each event within the respective host. Given the frequent assumption of very high mass progenitors for these explosions from various studies, most notably a direct progenitor detection, it is interesting to note the weak association of these subtypes with star formation as traced by H{\alpha} emission, particularly in comparison with type Ic supernovae, which trace the H{\alpha} emission and are thought to arise from high mass progenitors. The radial distributions of these transients compared to type Ic supernovae are also very different. This provides evidence for the growing hypothesis that these `interacting transients’ are in fact comprised of a variety of progenitor systems. The events contained within this sample are discussed in detail, where information in the literature exists, and compared to the environmental data provided. Impostors are found to split into two main classes, in terms of environment: SN2008S-like Impostors fall on regions of zero H{\alpha} emission, whereas {\eta}-Carina-like Impostors all fall on regions with positive H{\alpha} emission. We also find indications that the Impostor class originate from lower metallicity environments than type IIn, Ic and IIP SNe.

Physical properties and evolutionary state of the Lyman alpha emitting starburst galaxy IRAS 08339+6517

Though Lyman alpha emission (Lya) is one of the most used tracers of massive star formation at high redshift, a correct understanding of radiation transfer effects by neutral gas is required to properly quantify the star formation rate along the history of the Universe. We are embarked in a program to study the properties of the Lya emission (spectral profile, spatial distribution, relation to Balmer lines intensity,…) in several local starburst galaxies. We present here the results obtained for IRAS 08339+6517. Using evolutionary population synthesis models, we have characterized the properties of the starburst (UV continuum, Halpha, total infrared and X-ray emissions, etc.), which transformed 1.4e+8 Mo of gas into stars around 5-6 Myr ago. In addition to the central compact emission blob, we have identified a diffuse Lya emission component smoothly distributed over the whole central area of IRAS 08339+6517. This diffuse emission is spatially decoupled from the UV continuum, the Halpha emission or the Halpha/Hbeta ratio. Both locally and globally, the Lya/Halpha ratio is lower than the Case B predictions, even after reddening correction, with an overall Lya escape fraction of only 4%. We conclude that in IRAS 08339+6517 the resonant scattering of Lya photons by an outflowing shell of neutral gas causes their highly-efficient destruction by dust, which explains the low Lya escape fraction measured. These results stress again the importance of a proper correction of scattering and transfer effects when using Lya to derive the star formation rate in high-redshift galaxies.

A Stellar Census of the Tucana-Horologium Moving Group

We report the selection and spectroscopic confirmation of 129 new late-type (K3-M6) members of the Tuc-Hor moving group, a nearby (~40 pc), young (~40 Myr) population of comoving stars. We also report observations for 13/17 known Tuc-Hor members in this spectral type range, and that 62 additional candidates are likely to be unassociated field stars; the confirmation frequency for new candidates is therefore 129/191 = 67%. We have used RVs, Halpha emission, and Li6708 absorption to distinguish contaminants and bona fide members. Our expanded census of Tuc-Hor increases the known population by a factor of ~3 in total and by a factor of ~8 for members with SpT>K3, but even so, the K-M dwarf population of Tuc-Hor is still markedly incomplete. The spatial distribution of members appears to trace a 2D sheet, with a broad distribution in X and Y, but a very narrow distribution (+/-5 pc) in Z. The corresponding velocity distribution is very small, with a scatter of +/-1.1 km/s about the mean UVW velocity. We also show that the isochronal age (20–30 Myr) and the lithium depletion age (40 Myr) disagree, following a trend seen in other PMS populations. The Halpha emission follows a trend of increasing EW with later SpT, as seen for young clusters. We find that members have been depleted of lithium for spectral types of K7.0-M4.5. Finally, our purely kinematic and color-magnitude selection procedure allows us to test the efficiency and completeness for activity-based selection of young stars. We find that 60% of K-M dwarfs in Tuc-Hor do not have ROSAT counterparts and would be omitted in Xray selected samples. GALEX UV-selected samples using a previously suggested criterion for youth achieve completeness of 77% and purity of 78%. We suggest new selection criteria that yield >95% completeness for ~40 Myr populations.(Abridged)

Study of Dust and Ionized gas in Early-type Galaxies

We present results of optical broad-band and narrow-band Halpha observations of a sample of forty nearby early-type galaxies. The majority of sample galaxies are known to have dust in various forms viz. dust lanes, nuclear dust and patchy/filamentary dust. A detailed study of dust was performed for 12 galaxies with prominent dust features. The extinction curves for these galaxies run parallel to the Galactic extinction curve, implying that the properties of dust in these galaxies are similar to those of the Milky-Way. The ratio of total to selective extinction (Rv) varies between 2.1 and 3.8, with an average of 2.9 +/- 0.2, fairly close to its canonical value of 3.1 for our Galaxy. The average relative grain size <a>/a_Gal of dust particles in these galaxies turns out to be 1.01 +/- 0.2, while dust mass estimated using optical extinction lies in the range 10^2 to 10^4 M(sun) . The Halpha emission was detected in 23 out of 29 galaxies imaged through narrow- band filters with the Halpha luminosities in the range 10^38 – 10^41 erg s^-1. The mass of the ionized gas is in the range 10^3-10^5 M(sun). The morphology and extent of ionized gas is found similar to those of dust, indicating possible coexistence of dust and ionized gas in these galaxies. The absence of any apparent correlation between blue luminosity and normalized IRAS dust mass is suggestive of merger related origin of dust and gas in these galaxies.

Nature of H-alpha selected galaxies at z>2. II. Clumpy galaxies and compact star-forming galaxies

We present the morphological properties of 109 H\alpha-selected galaxies at z>2 in SXDF-UDS-CANDELS field. With high-resolution optical/near-infrared images obtained by Hubble Space Telescope, we identify giant clumps within the H\alpha emitters (HAEs). We find that at least 41% of our sample show clumpy structures in the underlying disks. The color gradient of clumps is commonly seen in the sense that the clumps near the galactic center tend to be redder than those in the outer regions. The mid-infrared detection in galaxies with red clumps and the spatial distribution of H\alpha emission suggest that dusty star-formation activity is probably occurring in the nuclear red clumps. A gas supply to a bulge component through the clump migration is one of the most potent physical processes to produce such dusty star-forming clumps and form massive bulges in local early-type galaxies. They would become large quiescent galaxies at later times just by consumption or blowout of remaining gas. Also, while most of the HAEs have extended disks, we observe two massive, compact HAEs, whose stellar surface densities are significantly higher. They are likely to be the direct progenitors of massive, compact quiescent galaxies at z=1.5-2.0. Two evolutionary paths to massive quiescent galaxies are devised to account for both the size growth of quiescent galaxies and their increased number density from z~2 to z=0.

H{\alpha} photometry of low mass stars in 47 Tucanae: chromospheric activity and exotica

We have used archival Hubble Space Telescope observations obtained with the Advanced Camera for Surveys to study the H{\alpha} emission properties of main sequence stars in the globular cluster 47 Tucanae. Using a combination of multi-band observations in the F606W, F814W and F658N bands, we search for stars showing H{\alpha} excess emission. An accurate photometric measurement of their H{\alpha} equivalent width allows us to identify objects with large H{\alpha} emission, which we attribute to mass accretion rather than enhanced chromospheric activity. The spatial position of some of these stars is coincident with that of known X-ray sources and their location in the colour-magnitude diagram allows us to classify them as active binaries or cataclysmic variables (CVs). We show that this method, commonly adopted to study accreting discs in young stellar objects, can be successfully used to identify and characterise candidate CVs.

OTS44: Disk and accretion at the planetary border

We discover that the very low-mass brown dwarf OTS44 (M9.5, ~12 M_Jup) has significant accretion and a substantial disk, which demonstrates that the processes that accompany canonical star formation occur down to a central mass of a few Jupiter masses. We discover in VLT/SINFONI spectra that OTS44 has strong, broad, and variable Paschen beta emission that is evidence for active accretion at the planetary border. We also detect strong Halpha emission of OTS44 in a literature spectrum and determine an Halpha EW (-141 A) that is indicative of active accretion. Both the Pa beta and Halpha emission lines have broad profiles with wings extending to velocities of about +/-200 km/s. We determine the mass accretion rate of OTS44 based on Halpha to 7.6×10^{-12} Msun/yr, which shows that OTS44 has a relatively high mass-accretion rate considering its small central mass. This mass rate is nevertheless consistent with the general decreasing trend found for stars of several solar masses down to brown dwarfs. Furthermore, we determine the properties of the disk surrounding OTS44 through radiative transfer modeling of flux measurement from the optical to the far-IR (Herschel) by applying a Bayesian analysis. We find that OTS44 has a highly flared disk (beta >1.2) with a mass of 9.1×10^{-5} M_Sun, i.e. about 0.1 M_Jup or 30 M_Earth. We show that the ratio of disk-to-central-mass of about 10^{-2} found for objects between 0.03 Msun and 14 Msun is also valid for OTS44 at a mass of ~0.01 M_Sun. Our observations are in line with an isolated star-like mode of the formation of brown dwarfs down to 0.01 M_Sun.

Macroclumping as solution of the discrepancy between H{\alpha} and P v mass loss diagnostics for O-type stars

Recent studies of O-type stars demonstrated that discrepant mass-loss rates are obtained when different diagnostic methods are employed – fitting the unsaturated UV resonance lines (e.g. P v) gives drastically lower values than obtained from the H{\alpha} emission. Wind clumping may be the main cause for this discrepancy. In a previous paper, we have presented 3-D Monte-Carlo calculations for the formation of scattering lines in a clumped stellar wind. In the present paper we select five O-type supergiants (from O4 to O7) and test whether the reported discrepancies can be resolved this way. In the first step, the analyses start with simulating the observed spectra with Potsdam Wolf-Rayet (PoWR) non-LTE model atmospheres. The mass-loss rates are adjusted to fit best to the observed H{\alpha} emission lines. For the unsaturated UV resonance lines (i.e. P v) we then apply our 3-D Monte-Carlo code, which can account for wind clumps of any optical depths, a non-void inter-clump medium, and a velocity dispersion inside the clumps. The ionization stratifications and underlying photospheric spectra are adopted from the PoWR models. From fitting the observed resonance line profiles, the properties of the wind clumps are constrained. Our results show that with the mass-loss rates that fit H{\alpha} (and other Balmer and He II lines), the UV resonance lines (especially the unsaturated doublet of P v) can also be reproduced without problem when macroclumping is taken into account. There is no need to artificially reduce the mass-loss rates, nor to assume a sub-solar phosphorus abundance or an extremely high clumping factor, contrary to what was claimed by other authors. These consistent mass-loss rates are lower by a factor of 1.3 to 2.6, compared to the mass-loss rate recipe from Vink et al. Macroclumping resolves the previously reported discrepancy between H{\alpha} and P v mass-loss diagnostics.

CFBDS J111807-064016: A new L/T transition brown dwarf in a binary system

Stellar-substellar binary systems are quite rare, and provide interesting benchmarks. They constrain the complex physics of substellar atmospheres, because several physical parameters of the substellar secondary can be fixed from the much better characterized main sequence primary. We report the discovery of CFBDS J111807-064016, a T2 brown dwarf companion to 2MASS J111806.99-064007.8, a low-mass M4.5-M5 star. The brown-dwarf was identified from the Canada France Brown Dwarf Survey. At a distance of 50-120 pc, the 7.7 arcsec angular separation corresponds to projected separations of 390-900 AU. The primary displays no Halpha emission, placing a lower limit on the age of the system of about 6 Gyr. The kinematics is also consistent with membership in the old thin disc. We obtained near-infrared spectra, which together with recent atmosphere models allow us determine the effective temperature and gravity of both components. From these parameters and the age constraint, evolutionary models estimate masses of 0.10 to 0.15 Msol for the M dwarf, and 0.06 to 0.07 Msol for the T dwarf. This system is a particularly valuable benchmark because the brown dwarf is an early T: the cloud-clearing that occurs at the L/T transition is very sensitive to gravity, metallicity, and detailed dust properties, and produces a large scatter in the colours. This T2 dwarf, with its metallicity measured from the primary and its mass and gravity much better constrained than those of younger early-Ts, will anchor our understanding of the colours of L/T transition brown dwarfs. It is also one of the most massive T dwarfs, just below the hydrogen-burning limit, and all this makes it a prime probe a brown dwarf atmosphere and evolution models.

Galaxy And Mass Assembly (GAMA): Resolving the role of environment in galaxy evolution

We present observations of 18 galaxies from the Galaxy And Mass Assembly (GAMA) survey made with the SPIRAL optical integral field unit (IFU) on the Anglo-Australian Telescope. The galaxies are selected to have a narrow range in stellar mass (6×10^9Msolar < M* <2×10^10 Msolar) in order to focus on the effects of environment. Local galaxy environments are measured quantitatively using 5th nearest neighbour surface densities. We find that the total star formation rates (SFR) measured from the IFU data are consistent with total SFRs measured from aperture correcting either GAMA or Sloan Digital Sky Survey single-fibre observations. The mean differences are SFR_GAMA/SFR_IFU = 1.26+/-0.23, sigma=0.90 and for the Sloan Digital Sky Survey we similarly find SFR_Brinchmann/SFR_IFU = 1.34+/-0.17, sigma=0.67. Examining the relationships with environment, we find off-centre and clumpy Halpha emission is not significantly dependent on environment, being present in 2/7 (29^+20_-11 per cent) galaxies in high-density environments (>0.77 Mpc^-2), and 5/11 (45^+15_-13 per cent) galaxies in low-density environments (<0.77 Mpc^-2). We find a weak but not significant relationship of the total star formation rates of star-forming galaxies with environment. Due to the size of our sample and the scatter observed we do not draw a definitive conclusion about a possible SFR dependence on environment. Examining the spatial distribution of the Halpha emission, we find no evidence for a change in shape or amplitude of the radial profile of star-forming galaxies with environment. If these observations are borne out in larger samples this would infer that any environment-driven star-formation suppression must either act very rapidly (the `infall-and-quench’ model) or that galaxies must evolve in a density-dependent manner (an `in-situ evolution’ model).

A New Halpha Emission-Line Survey in the Orion Nebula Cluster

We present results from an Halpha emission-line survey in a one square degree area centered on the Orion Nebula Cluster, obtained with the Wide Field Grism Spectrograph-2 on the 2.2-meter telescope of the University of Hawaii. We identified 587 stars with Halpha emission, 99 of which, located mainly in the outer regions of the observed area, have not appeared in previous Halpha surveys. We determined the equivalent width (EW) of the line, and based on it classified 372 stars as classical T Tauri stars (CTTS) and 187 as weak line T Tauri stars (WTTS). Simultaneous r’, i’ photometry indicates a limiting magnitude of r’ ~ 20 mag, but the sample is incomplete at r’ > 17 mag. The surface distribution of the Halpha emission stars reveals a clustered and a dispersed population, the former consisting of younger and more massive young stars than the latter. Comparison of the derived EWs with those found in the literature indicates variability of the Halpha line. We found that the typical amplitudes of the variability are not greater than a factor 2-3 in the most cases. We identified a subgroup of low-EW stars with infrared signatures indicative of optically thick accretion disks. We studied the correlations between the equivalent width and other properties of the stars. Based on literature data we examined several properties of our CTTS and WTTS subsamples and found significant differences in mid-infrared color indices, average rotational periods, and spectral energy distribution characteristics of the subsamples.

Pre-main sequence stars older than 8 Myr in the Eagle Nebula

Attention is given to a population of 110 stars in the NGC 6611 cluster of the Eagle Nebula that have prominent near-infrared (NIR) excess and optical colours typical of pre-main sequence (PMS) stars older than 8 Myr. At least half of those for which spectroscopy exists have a Halpha emission line profile revealing active accretion. In principle, the V-I colours of all these stars would be consistent with those of young PMS objects (< 1 Myr) whose radiation is heavily obscured by a circumstellar disc seen at high inclination and in small part scattered towards the observer by the back side of the disc. However, using theoretical models it is shown here that objects of this type can only account for a few percent of this population. In fact, the spatial distribution of these objects, their X-ray luminosities, their optical brightness, their positions in the colour-magnitude diagram and the weak Li absorption lines of the stars studied spectroscopically suggest that most of them are at least 8 times older than the ~1 Myr-old PMS stars already known in this cluster and could be as old as ~30 Myr. This is the largest homogeneous sample to date of Galactic PMS stars considerably older than 8 Myr that are still actively accreting from a circumstellar disc and it allows us to set a lower limit of 7% to the disc frequency at ~16 Myr in NGC 6611. These values imply a characteristic exponential lifetime of ~6 Myr for disc dissipation.

Photometric evolution, orbital modulation and progenitor of Nova Mon 2012

We present and discuss accurate and densely mapped BVRI lightcurves of the neon Nova Mon 2012, supplemented by the evolution in Stromgren b and y bands and in the integrated flux of relevant emission lines. Our monitoring started with the optical discovery of the nova and extend to day +270, well past the end of the super-soft phase in X-rays. The nova displayed very smoothly evolving lightcurves. A bifurcation between y and V light-curves took place at the start of the SSS phase, and a knee developed toward the end of the SSS phase. The apparent magnitude of the nova at the unobserved optical maximum is constrained to +2.8=<V=<4.2. The appearance, grow in amplitude and then demise of a 0.29585 (+/-0.00002) days orbital modulation of the optical brightness was followed along the nova evolution. The observed modulation has a near-sinusoidal shape and a weak secondary minimum at phase 0.5. We favor an interpretation in terms of super-imposed ellipsoidal distortion of the Roche lobe filling companion and irradiation of its side facing the WD. Similar lightcurves are typical of symbiotic stars where a Roche lobe filling giant is irradiated by a very hot WD. Given the high orbital inclination, mutual occultation between the donor star and the accretion disk could contribute to the observed modulation. The optical+infrared spectral energy distribution of Nova Mon 2012 during the quiescence preceeding the outburst is nicely fitted by a early K-type main-sequence star (~K3V) at 1.5 kpc distance, reddened by E(B-V)=0.38, with a WD companion and an accretion disk contributing to the observed blue excess and moderate Halpha emission. A typical early K-type main-sequence star with a mass of ~0.75 Msun and a radius of ~0.8 Rsun, would fill its Roche lobe for a P=0.29585 day orbital period and a more massive WD companion.

Enhanced Halpha activity at periastron in the young and massive spectroscopic binary HD200775

Young close binaries clear central cavities in their surrounding circumbinary disk from which the stars can still accrete material. This process takes place within the very first astronomical units, and is still not well constrained as the observational evidence has been gathered, until now, only by means of spectroscopy. The young object HD200775 (MWC361) is a massive spectroscopic binary (separation of ~15.9mas, ~5.0~AU), with uncertain classification (early/late Be), that shows a strong and variable Halpha emission. We aim to study the mechanisms that produce the Halpha line at the AU-scale. Combining the radial velocity measurements and astrometric data available in the literature, we determined new orbital parameters. With the VEGA instrument on the CHARA array, we spatially and spectrally resolved the Halpha emission of HD200775, at low and medium spectral resolutions (R~1600 and 5000) over a full orbital period (~3.6 years). We observe that the Halpha equivalent width varies with the orbital phase, and increases close to periastron, as expected from theoretical models that predict an increase of the mass transfer from the circumbinary disk to the primary disk. In addition, using spectral visibilities and differential phases, we find marginal variations of the typical extent of the Halpha emission (at 1 to 2-sigma level) and location (at 1 to 5-sigma level). The spatial extent of the Halpha emission, as probed by a Gaussian FWHM, is minimum at the ascending node (0.67+/-0.20 mas, i.e., 0.22+/-0.06 AU), and more than doubles at periastron. In addition, the Gaussian photocenter is slightly displaced in the direction opposite to the secondary, ruling out the scenario in which all or most of the Halpha emission is due to accretion onto the secondary. These findings, together with the wide Halpha line profile, may be due to a non-spherical wind enhanced at periastron.

A remarkable sample of new symbiotic stars towards the Galactic Bulge

Symbiotic stars are the longest orbital period interacting binaries, where nova-like outbursts are generated by the accretion of a high mass loss rate red giant wind onto a white dwarf companion. Long-term photometric monitoring surveys such as OGLE and MACHO are ideal platforms to identify nova-like events in symbiotic stars, however there are only a handful of known systems within the small footprint of these surveys. We introduce a systematic Halpha emission line object survey for new symbiotic stars covering 35 deg^2 towards the Galactic Bulge that combines deep 2dF/AAOmega spectroscopy with OGLE and MACHO photometry. This powerful combination has uncovered nearly two dozen new symbiotic stars, more than a dozen probable symbiotic stars, and several other unusual Halpha emission line stars. While we don’t find any nova-like activity, the lightcurves do exhibit semi-regular and Mira pulsations, orbital variations and slower changes due to dust. Here we introduce a few of the new symbiotics, including H1-45, only the fourth known carbon symbiotic Mira. This remarkable discovery may be the first luminous carbon star belonging to the Galactic Bulge, according to its period-luminosity relation distance of 6.2+-1.4 kpc, potentially shedding new light on the puzzling lack of luminous carbon stars in the Bulge. We also present two old novae captured in the nebular phase, complementing other surveys to better characterise the old nova population.

Symbiotic stars and other Halpha emission line stars towards the Galactic Bulge

Symbiotic stars are interacting binaries with the longest orbital periods and their multi-component structure makes them rich astrophysical laboratories. The accretion of a high mass loss rate red giant wind on to a white dwarf (WD) makes them promising Type Ia supernovae (SNe Ia) progenitors. Systematic surveys for new Galactic symbiotic stars are critical to identify new promising SNe Ia progenitors (e.g. RS Oph) and to better estimate the total population size to compare against SNe Ia rates. Central to the latter objective is building a complete census of symbiotic stars towards the Galactic Bulge. Here we report on the results of a systematic survey of Halpha emission line stars covering 35 deg^2. It is distinguished by the combination of deep optical spectroscopy and long-term lightcurves that improve the certainty of our classifications. A total of 20 bona-fide symbiotic stars are found (13 S-types, 6 D-types and 1 D’-type), 35% of which show the symbiotic specific Raman-scattered OVI emission bands, as well as 15 possible symbiotic stars that require further study (6 S-types and 9 D-types). Lightcurves show a diverse range of variability including stellar pulsations (semi-regular and Mira), orbital variations and slow changes due to dust. Orbital periods are determined for 5 S-types and pulsation periods for 3 D-types. The most significant D-type found is H1-45 and its carbon Mira with a pulsation period of 408.6 days, corresponding to a distance of ~6.2+-1.4 kpc and M_K=-8.06+-0.12 mag. If H1-45 belongs to the Galactic Bulge, then it would be the first bona-fide luminous Galactic Bulge carbon star. The lack of luminous carbon stars in the Bulge is a longstanding unsolved problem. A possible explanation for H1-45 may be that the carbon enhancement was accreted from the progenitor of the WD companion. A wide variety of unusual emission line stars were also identified. (abridged)

Studying the kinematics of the giant star-forming region 30 Doradus. I. The data

We present high-quality VLT-FLAMES optical spectroscopy of the nebular gas in the giant star-forming region 30 Doradus. In this paper, the first of a series, we introduce our observations and discuss the main kinematic features of 30 Dor, as revealed by the spectroscopy of the ionized gas in the region. The primary data set consists of regular grid of nebular observations, which we used to produce a spectroscopic datacube of 30 Dor, centered on the massive star cluster R136 and covering a field-of-view of 10′x10′. The main emission lines present in the datacube are from Halpha and [NII]6548,6584. The Halpha emission-line profile varies across the region from simple single-peaked emission to complex, multiple-component profiles, suggesting that different physical mechanisms are acting on the excited gas. To analyse the gas kinematics we fit Gaussian profiles to the observed Halpha features. Unexpectedly, the narrowest Halpha profile in our sample lies close to the supernova remnant 30 Dor B. We present maps of the velocity field and velocity dispersion across 30 Dor, finding five previously unclassified expanding structures. These maps highlight the kinematic richness of 30 Dor (e.g. supersonic motions), which will be analysed in future papers.

HALOGAS: Extraplanar gas in NGC 3198

We present the analysis of new, deep HI observations of the spiral galaxy NGC 3198, as part of the HALOGAS (Westerbork Hydrogen Accretion in LOcal GAlaxieS) survey, with the main aim of investigating the presence, amount, morphology and kinematics of extraplanar gas. We present models of the HI observations of NGC 3198: the model that matches best the observed data cube features a thick disk with a scale height of ~3 kpc and an HI mass of about 15% of the total HI mass; this thick disk also has a decrease in rotation velocity as a function of height (lag) of 7-15 km/s/kpc (though with large uncertainties). This extraplanar gas is detected for the first time in NGC 3198. Radially, this gas appears to extend slightly beyond the actively star-forming body of the galaxy (as traced by the Halpha emission), but it is not more radially extended than the outer, fainter parts of the stellar disk. Compared to previous studies, thanks to the improved sensitivity we trace the rotation curve out to larger radii. We model the rotation curve in the framework of MOND (Modified Newtonian Dynamics) and we confirm that, with the allowed distance range we assumed, fit quality is modest in this galaxy, but the new outer parts are explained in a satisfactory way.

Kinematics of the intermediate mass black hole candidate HLX-1

We studied the optical spectrum of HLX-1 during its latest outburst, using the FORS2 spectrograph on the Very Large Telescope. We detect an Halpha emission line centered at lambda = (6718.9 +/- 0.9) Ang and find that its projected radial velocity with respect to the nucleus of ESO243-49 is (424 +/- 27) km/s, while the maximum rotational velocity of the stars in that galaxy is ~209 km/s. This suggests that HLX-1 and its surrounding stars were not formed in situ, but came either from a disrupted dwarf galaxy or from a nuclear recoil. We also find that the Halpha emission line is resolved with full width at half maximum ~400 km/s, suggesting a nebular rather than disk origin for the emission. Its luminosity (L_{Halpha} ~ a few 10^{37} erg/s, equivalent width ~70 Ang) is also consistent with emission from a nebula photo-ionized by HLX-1.

A binary scenario for the pre-explosion outburst of the supernova 2010mc

I raise the possibility that the pre-explosion outburst (PEO) of the type IIn supernova 2010mc (PTF 10tel) was energized by mass accretion onto an O main-sequence stellar companion. According to this suggestion the SN progenitor suffered a rapid expansion within months before explosion. The expansion was driven by leakage of energy from the core where vigorous oxygen nuclear burning takes place within a year prior to explosion. This expansion triggered mass transfer onto the secondary star. Most of the extra energy of the outburst comes from the accretion of ~0.1Mo onto the secondary star. As well, the gas outflowing at v~2000 km/s was launched from the accreting secondary star, most likely in a bipolar outflow. The binary model can account for the slower circumstellar medium that was ejected at earlier times, and explain the red-shifted peak of the Halpha emission at 5.8 days past explosion. I compare some properties of the PEO of SN 2010mc to those of other stellar eruptions, such as the stellar merger event V838 Monocerotis and the nineteenth century Great Eruption of the massive stellar binary system Eta Carinae. I speculate that all Type IIn supernovae owe their dense circumstellar gas to binary interaction.

CV1 in the globular cluster M 22: confirming its nature through X-ray observations and optical spectroscopy

Context. Observations of cataclysmic variables in globular clusters appear to show a dearth of outbursts compared to those observed in the field. A number of explanations have been proposed, including low mass-transfer rates and/or moderate magnetic fields implying higher mass white dwarfs than the average observed in the field. Alternatively this apparent dearth may be simply a selection bias. Aims. We examine multi-wavelength data of a new cataclysmic variable, CV1, in the globular cluster M 22 to try to constrain its period and magnetic nature, with an aim at understanding whether globular cluster cataclysmic variables are intrinsically different from those observed in the field. Methods. We use the sub-arcsecond resolution of the Chandra ACIS-S to identify the X-ray counterpart to CV1 and analyse the X-ray spectrum to determine the spectral model that best describes this source. We also examine the low resolution optical spectrum for emission lines typical of cataclysmic variables. Cross correlating the Halpha line in each individual spectrum also allows us to search for orbital motion. Results. The X-ray spectrum reveals a source best-fitted with a high-temperature bremsstrahlung model and an X-ray unabsorbed luminosity of 1.8e32 erg/s (0.3-8.0 keV), which are typical of cataclysmic variables. Optical spectra reveal Balmer emission lines, which are indicative of an accretion disc. Potential radial velocity in the Halpha emission line is detected and a period for CV1 is proposed. Conclusions. These observations support the CV identification. The radial velocity measurements suggest that CV1 may have an orbital period of ~7 hours, but further higher resolution optical spectroscopy of CV1 is needed to unequivocally establish the nature of this CV and its orbital period.

Discovery of an Halpha emitting disk around the supermassive black hole of M31

Due to its proximity, the mass of the supermassive black hole in the nucleus of Andromeda galaxy (M31), the most massive black hole in the Local Group of galaxies, has been measured by several methods involving the kinematics of a stellar disk that surrounds it. We report here the discovery of an eccentric Halpha emitting disk around the black hole at the center of M31 and show how modeling this disk can provide an independent determination of the mass of the black hole. Our model implies a mass of 5.0_{-1.0}^{+0.8} x 10^7 Mo for the central black hole, consistent with the average of determinations by methods involving stellar dynamics, and compatible (at 1-sigma level) with measurements obtained from the most detailed models of the stellar disk around the central black hole. This value is also consistent with the M-sigma relation. In order to make a comparison, we applied our simulation on the stellar kinematics in the nucleus of M31 and concluded that the parameters obtained for the stellar disk are not formally compatible with the parameters obtained for the Halpha emitting disk. This result suggests that the stellar and the Halpha emitting disks are intrinsically different from each other. A plausible explanation is that the Halpha emission is associated with a gaseous disk. This hypothesis is supported by the detection of traces of weaker nebular lines in the nuclear region of M31. However, we cannot exclude the possibility that the Halpha emission is, at least partially, generated by stars.

Carbon monoxide in the environs of the star WR 16

We analyze the carbon monoxide emission around the star WR 16 aiming to chieve a better understanding of the interaction between massive stars with their surroundings. We study the molecular gas in a region of 86.’4 x 86.’4 in size using CO (J=1-0) and 13CO (J=1-0) line data obtained with the 4-m NANTEN telescope. Radio continuum archival data at 4.85 GHz, obtained from the Parkes-MIT-NRAO Southern Radio Survey, are also analyzed to account for the ionized gas. Available IRAS (HIRES) 60 and 100 microns images are used to study the characteristics of the dust around the star. Our new CO and 13CO data allow the low/intermediate density molecular gas surrounding the WR nebula to be completely mapped. We report two molecular features at -5 km/s and -8.5 km/s (component 1 and component 2, respectively) having a good morphological resemblance with the Halpha emission of the ring nebula. Component 2 seems to be associated with the external ring, whilst component 1 is placed at the interface between component 2 and the Halpha emission. We also report a third molecular feature 10′ in size (component 3) at a velocity of -9.5 km/s having a good morphological correspondence with the inner optical and IR emission, although high resolution observations are recommended to confirm its existence. The stratified morphology and kinematics of the molecular gas could be associated to shock fronts and high mass-loss events related to different evolutive phases of the WR star, which have acted upon the surrounding circumstellar molecular gas. An analysis of the mass of component 1 suggests that this feature is composed by swept-up interstellar gas and is probably enriched by molecular ejecta. The direction of the proper motion of WR 16 suggests that the morphology of the inner ring nebula is induced by the stellar motion.

Integrated Spectroscopy of the Herschel Reference Survey. The spectral line properties of a volume-limited, K-band selected sample of nearby galaxies

We present long-slit integrated spectroscopy of 238 late-type galaxies belonging to the Herschel Reference Survey, a volume limited sample representative of the nearby universe. This sample has a unique legacy value since ideally defined for any statistical study of the multifrequency properties of galaxies spanning a large range in morphological type and luminosity. The spectroscopic observations cover the spectral range 3600-6900 A at a resolution R ~ 1000 and are thus suitable for separating the underlying absorption from the emission of the Hbeta line as well as the two [NII] lines from the Halpha emission. We measure the fluxes and the equivalent widths of the strongest emission lines ([OII], Hbeta, [OIII], [NII], Halpha, and [SII]). The data are used to study the distribution of the equivalent width of all the emission lines, of the Balmer decrement C(Hbeta) and of the observed underlying Balmer absorption under Hbeta in this sample. Combining these new spectroscopic data with those available at other frequencies, we also study the dependence of C(Hbeta) and E.W.Hbeta_{abs} on morphological type, stellar mass and stellar surface density, star formation rate, birthrate parameter and metallicity in galaxies belonging to different environments (fields vs. Virgo). The distribution of the equivalent width of all the emission lines, of C(Hbeta) and E.W.Hbeta_{abs} are systematically different in cluster and field galaxies. The Balmer decrement increases with stellar mass, stellar surface density, metallicity and star formation rate of the observed galaxies, while it is unexpectedly almost independent from the column density of the atomic and molecular gas. The dependence of C(Hbeta) on stellar mass is steeper than that previously found in other works. The underlying Balmer absorption does not significantly change with any of these physical parameters.

NGC6240: extended CO structures and their association with shocked gas

We present deep CO observations of NGC6240 performed with the IRAM Plateau de Bure Interferometer (PdBI). NGC6240 is the prototypical example of a major galaxy merger in progress, caught at an early stage, with an extended, strongly-disturbed butterfly-like morphology and the presence of a heavily obscured active nucleus in the core of each progenitor galaxy. The CO line shows a skewed profile with very broad and asymmetric wings detected out to velocities of -600 km/s and +800 km/s with respect to the systemic velocity. The PdBI maps reveal the existence of two prominent structures of blueshifted CO emission. One extends eastward, i.e. approximately perpendicular to the line connecting the galactic nuclei, over scales of ~7 kpc and shows velocities up to -400 km/s. The other extends southwestward out to ~7 kpc from the nuclear region, and has a velocity of -100 km/s with respect to the systemic one. Interestingly, redshifted emission with velocities 400 to 800 km/s is detected around the two nuclei, extending in the east-west direction, and partly overlapping with the eastern blue-shifted structure, although tracing a more compact region of size ~1.7 kpc. The overlap between the southwestern CO blob and the dust lanes seen in HST images, which are interpreted as tidal tails, indicates that the molecular gas is deeply affected by galaxy interactions. The eastern blueshifted CO emission is co-spatial with an Halpha filament that is associated with strong H2 and soft X-ray emission. The analysis of Chandra X-ray data provides strong evidence for shocked gas at the position of the Halpha emission. Its association with outflowing molecular gas supports a scenario where the molecular gas is compressed into a shock wave that propagates eastward from the nuclei. If this is an outflow, the AGN are likely the driving force.

Optical photometric monitoring of gamma-ray binaries

Four gamma-ray binaries, namely PSR B1259-63, HESS J0632+057, HD 215227 and LS I +61 303, contain compact objects orbiting around massive Be stars. The nature of the compact object is only known in the case of PSR B1259-63, but the other systems could also contain young non-accreting pulsars with relativistic winds. Around periastron passage the compact objects should produce significant changes in the structure of the Be discs due to gravitational forces and eventually by ram pressure from the putative pulsar wind. Indeed, variability in the Halpha emission line has been detected in all these systems, and periodic variability in the optical photometry has been detected in two of them. However, there is lack of a systematic monitoring with accurate photometry, which could be used to constrain the shape of the disc during the periastron passage. This information is important to build accurate physical models to explain the broadband spectral energy distribution of these sources. Here we present an ongoing program to monitor the optical photometry of gamma-ray binaries and we show preliminary results for the case of HD 215227.

The Nature of Starbursts: III. The Spatial Distribution of Star Formation

We map the spatial distribution of recent star formation over a few x 100 Myr timescales in fifteen starburst dwarf galaxies using the location of young blue helium burning stars identified from optically resolved stellar populations in archival Hubble Space Telescope observations. By comparing the star formation histories from both the high surface brightness central regions and the diffuse outer regions, we measure the degree to which the star formation has been centrally concentrated during the galaxies’ starbursts, using three different metrics for the spatial concentration. We find that the galaxies span a full range in spatial concentration, from highly centralized to broadly distributed star formation. Since most starbursts have historically been identified by relatively short timescale star formation tracers (e.g., Halpha emission), there could be a strong bias towards classifying only those galaxies with recent, centralized star formation as starbursts, while missing starbursts that are spatially distributed.

Star formation activity in the Galactic H II region Sh2-297

We present a multiwavelength study of the Galactic H II region Sh2-297, located in Canis Major OB1 complex. Optical spectroscopic observations are used to constrain the spectral type of ionizing star HD 53623 as B0V. The classical nature of this H II region is affirmed by the low values of electron density and emission measure, which are calculated to be 756 cm^-3 and 9.15 x 10^5 cm^-6 pc using the radio continuum observations at 610 and 1280 MHz, and VLA archival data at 1420 MHz. To understand local star formation, we identified the young stellar object (YSO) candidates in a region of area ~ 7.5′ x 7.5′ centered on Sh2-297 using grism slitless spectroscopy (to identify the Halpha emission line stars), and near infrared (NIR) observations. NIR YSO candidates are further classified into various evolutionary stages using color-color (CC) and color-magnitude (CM) diagrams, giving 50 red sources (H-K > 0.6) and 26 Class II-like sources. The mass and age range of the YSOs are estimated to be ~ 0.1 – 2 Msolar and 0.5 – 2 Myr using optical (V/V-I) and NIR (J/J-H) CM diagrams. The mean age of the YSOs is found to be ~ 1 Myr, which is of the order of dynamical age of 1.07 Myr of the H II region. Using the estimated range of visual extinction (1.1 – 25 mag) from literature and NIR data for the region, spectral energy distribution (SED) models have been implemented for selected YSOs which show masses and ages to be consistent with estimated values. The spatial distribution of YSOs shows an evolutionary sequence, suggesting triggered star formation in the region. The star formation seems to have propagated from the ionizing star towards the cold dark cloud LDN1657A located west of Sh2-297.

Correcting for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs

We present empirical relations for determining the amount by which the effective temperatures and radii—and therefore the estimated masses—of low-mass stars and brown dwarfs are altered due to chromospheric activity. Accurate estimates of stellar radii are especially important in the context of searches for transiting exoplanets, which rely upon the assumed stellar radius/density to infer the planet radius/density. Our relations are based on a large set of well studied low-mass stars in the field and on a set of benchmark low-mass eclipsing binaries. The relations link the amount by which an active object’s temperature is suppressed, and its radius inflated, to the strength of its Halpha emission. These relations are found to approximately preserve bolometric luminosity. We apply these relations to the peculiar brown-dwarf eclipsing binary 2M0535-05, in which the active, higher-mass brown dwarf has a cooler temperature than its inactive, lower-mass companion. The relations correctly reproduce the observed temperatures and radii of 2M0535-05 after accounting for the Halpha emission; 2M0535-05 would be in precise agreement with theoretical isochrones were it inactive. The relations that we present are applicable to brown dwarfs and low-mass stars with masses below 0.8 Msun and for which the activity, as measured by Halpha, is in the range -4.6 < log Lha/Lbol < -3.3. We expect these relations to be most useful for correcting radius and mass estimates of low-mass stars and brown dwarfs over their active lifetimes (few Gyr). We also discuss the implications of this work for determinations of young cluster IMFs.

Spectroscopy of Very Low Mass Stars and Brown Dwarfs in the Lambda Orionis Star Forming Region

Context. Most observational studies so far point towards brown dwarfs sharing a similar formation mechanism as the one accepted for low mass stars. However, larger databases and more systematic studies are needed before strong conclusions can be reached. Aims. In this second paper of a series devoted to the study of the spectroscopic properties of the members of the Lambda Orionis Star Forming Region, we study accretion, activity and rotation for a wide set of spectroscopically confirmed members of the central star cluster Collinder 69 to draw analogies and/or differences between the brown dwarf and stellar populations of this cluster. Moreover, we present comparisons with other star forming regions of similar and different ages to address environmental effects on our conclusions. Methods. We study prominent photospheric lines to derive rotational velocities and emission lines to distinguish between accretion processes and chromospheric activity. In addition, we include information about disk presence and X-ray emission. Results. We report very large differences in the disk fractions of low mass stars and brown dwarfs (~58%) when compared to higher mass stars (26+4-3%) with 0.6 Msun being the critical mass we find for this dichotomy. As a byproduct, we address the implications of the spatial distribution of disk and diskless members in the formation scenario of the cluster itself. We have used the Halpha emission to discriminate among accreting and non-accreting sources finding that 38+8-7% of sources harboring disks undergo active accretion and that his percentage stays similar in the substellar regime. For those sources we have estimated accretion rates. Finally, regarding rotational velocities, we find a high dispersion in vsin(i) which is even larger among the diskless population.

Discovery of optical candidate supernova remnants in Sagittarius

During an [O III] survey for planetary nebulae, we identified a region in Sagittarius containing several candidate Supernova Remnants and obtained deep optical narrow-band images and spectra to explore their nature. The images of the unstudied area have been obtained in the light of Halpha+[N II], [S II] and [O III]. The resulting mosaic covers an area of 1.4×1.0 deg^2 where filamentary and diffuse emission was discovered, suggesting the existence of more than one supernova remnants (SNRs) in the area. Deep long slit spectra were also taken of eight different regions. Both the flux calibrated images and the spectra show that the emission from the filamentary structures originates from shock-heated gas, while the photo-ionization mechanism is responsible for the diffuse emission. Part of the optical emission is found to be correlated with the radio at 4850 MHz suggesting their association, while the WISE infrared emission found in the area at 12 and 22 micron marginally correlates with the optical. The presence of the [O III] emission line in one of the candidate SNRs suggests shock velocities into the interstellar "clouds" between 120 and 200 km/s, while the absence in the other indicates slower shock velocities. For all candidate remnants the [S II] 6716/6731 ratio indicates electron densities below 240 cm^{-3}, while the Halpha emission has been measured to be between 0.6 to 41×10^{-17} erg/s/cm^2/arcsec^2. The existence of eight pulsars within 1.5deg away from the center of the candidate SNRs also supports the scenario of many SNRs in the area as well as that the detected optical emission could be part of a number of supernovae explosions.

An Empirical Correction for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs [Replacement]

We present empirical relations for determining the amount by which the effective temperatures and radii — and therefore the estimated masses — of low-mass stars and brown dwarfs are altered due to chromospheric activity. We base our relations on a large set of low-mass stars in the field with Halpha activity measurements, and on a set of low-mass eclipsing binaries with X-ray activity measurements from which we indirectly infer the Halpha activity. Both samples yield consistent relations linking the amount by which an active object’s temperature is suppressed, and its radius inflated, to the strength of its Halpha emission. These relations are found to approximately preserve bolometric luminosity. We apply these relations to the peculiar brown-dwarf eclipsing binary 2M0535-05, in which the active, higher-mass brown dwarf has a cooler temperature than its inactive, lower-mass companion. The relations correctly reproduce the observed temperatures and radii of 2M0535-05 after accounting for the Halpha emission; 2M0535-05 would be in precise agreement with theoretical isochrones were it inactive. The relations that we present are applicable to brown dwarfs and low-mass stars with masses below 0.8 Msun and for which the activity, as measured by the fractional Halpha luminosity, is in the range -4.6 < log LHa/Lbol < -3.3. We expect these relations to be most useful for correcting radius and mass estimates of low-mass stars and brown dwarfs over their active lifetimes (few Gyr) and when the ages or distances (and therefore luminosities) are unknown. We also discuss the implications of this work for improved determinations of young cluster initial mass functions.

An Empirical Correction for Activity Effects on the Temperatures, Radii, and Estimated Masses of Low-Mass Stars and Brown Dwarfs

We present an empirical relations for correcting the estimated masses, effective temperatures, and radii of chromospherically active low-mass stars and brown dwarfs. We base our corrections on a large set of low-mass stars in the field with Halpha activity measurements, and on a set of low-mass eclipsing binaries with X-ray activity measurements from which we indirectly infer the Halpha activity. Both samples yield consistent relations linking the amount by which an active object’s temperature is suppressed, and the amount by which its radius is inflated, to the strength of its Halpha emission. Bolometric luminosity is found to be approximately preserved by these temperature and radius corrections. We apply these relations to the peculiar brown-dwarf eclipsing binary 2M0535-05, in which the active, higher-mass brown dwarf has a cooler temperature than its inactive, lower-mass companion. We find that the Halpha-corrected temperatures bring the inferred masses of the brown dwarfs into agreement with theoretical isochrones. These empirical relations are applicable to brown dwarfs and low-mass stars with masses below 0.8 Msun and for which the activity, as measured by the fractional Halpha luminosity, is in the range -4.6 < log LHa/Lbol < -3.3. We expect these corrections to be most useful for improving temperatures and radii of low-mass stars and brown dwarfs over their active lifetimes (few Gyr) and thereby also the inferred masses of objects with unknown ages or distances (and therefore unknown luminosities). We also discuss the implications of this work for improved determinations of young cluster initial mass functions.

A Uniformly Selected Sample of Low-mass Black Holes in Seyfert 1 Galaxies

We have conducted a systematic search of low-mass black holes (BHs) in active galactic nuclei (AGNs) with broad Halpha emission lines, aiming at building a homogeneous sample that is more complete than previous ones for fainter, less highly accreting sources. For this purpose, we developed a set of elaborate, automated selection procedures and applied it uniformly to the Fourth Data Release of the Sloan Digital Sky Survey. Special attention is given to AGN–galaxy spectral decomposition and emission-line deblending. We define a sample of 309 type 1 AGNs with BH masses in the range $8 \times 10^4$–$2 \times 10^6$ \msun (with a median of $1.2 \times 10^6$ solar mass), using the virial mass estimator based on the broad Halpha line. About half of our sample of low-mass BHs differs from that of Greene & Ho, with 61 of them discovered here for the first time. Our new sample picks up more AGNs with low accretion rates: the Eddington ratios of the present sample range from $<~0.01$ to ~1, with 30% below 0.1. This suggests that a significant fraction of low-mass BHs in the local Universe are accreting at low rates. The host galaxies of the low-mass BHs have luminosities similar to those of $L^*$ field galaxies, optical colors of Sbc spirals, and stellar spectral features consistent with a continuous star formation history with a mean stellar age of less than 1 Gyr.

A Stellar Mass Threshold for Quenching of Field Galaxies [Replacement]

We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a re-analysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star forming dwarf galaxies, defining quenched galaxies as having no Halpha emission (EW_Halpha < 2 AA) and a strong 4000AA-break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M_stellar < 1.0×10^9 Msun below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1-sigma upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0×10^9 Msun, ending star-formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.

Star formation in bulgeless late type galaxies: clues to their evolution

We present GMRT 1280 MHz radio continuum observations and follow-up optical studies of the disk and nuclear star formation in a sample of low luminosity bulgeless galaxies. The main aim is to understand bulge formation and overall disk evolution in these late type galaxies. We detected radio continuum from five of the twelve galaxies in our sample; the emission is mainly associated with disk star formation. Only two of the detected galaxies had extended radio emission; the others had patchy disk emission. In the former two galaxies, NGC3445 and NGC4027, the radio continuum is associated with star formation triggered by tidal interactions with nearby companion galaxies. We did follow-up Halpha imaging and nuclear spectroscopy of both galaxies using the Himalayan Chandra Telescope (HCT). The Halpha emission is mainly associated with the strong spiral arms. The nuclear spectra indicate ongoing nuclear star formation in NGC3445 and NGC4027 which maybe associated with nuclear star clusters. No obvious signs of AGN activity were detected. Although nearly bulgeless, both galaxies appear to have central oval distortions in the R band images; these could represent pseudobulges that may later evolve into large bulges. We thus conclude that tidal interactions are an important means of bulge formation and disk evolution in bulgeless galaxies; without such triggers these galaxies appear to be low in star formation and overall disk evolution.

On how leakage can affect the Star Formation Rate estimation using Halpha luminosity

We present observational evidence that leakage of ionising photons from star-forming regions can affect the quantification of the star formation rate (SFR) in galaxies. This effect could partially explain the differences between the SFR estimates using the far ultraviolet (FUV) and the Halpha emission. We find that leakage could decrease the SFR(Ha)/SFR(FUV) ratio by up to a 25 per cent. The evidence is based on the observation that the SFR(Ha)/SFR(FUV) ratio is lower for objects showing a shell Halpha structure than for regions exhibiting a much more compact morphology. The study has been performed on three object samples: low luminosity dwarf galaxies from the Local Volume Legacy survey and star-forming regions in the Large Magellanic Cloud and the nearby Local Group galaxy M33. For the three samples we find differences (1.1-1.4sigma) between the SFR(Ha)/SFR(FUV) for compact and shell objects. Although leakage cannot entirely explain the observed trend of SFR(Ha)/SFR(FUV) ratios for systems with low SFR, we show the mechanism can lead to different SFR estimates when using Halpha and FUV luminosities. Therefore, further study is needed to constrain the contribution of leakage to the low SFR(Ha)/SFR(FUV) ratios observed in dwarf galaxies and its impact on the Halpha flux as a SFR indicator in such objects.

A dynamical magnetosphere model for periodic Halpha emission from the slowly rotating magnetic O star HD191612

The magnetic O-star HD191612 exhibits strongly variable, cyclic Balmer line emission on a 538-day period. We show here that its variable Halpha emission can be well reproduced by the rotational phase variation of synthetic spectra computed directly from full radiation magneto-hydrodynamical simulations of a magnetically confined wind. In slow rotators such as HD191612, wind material on closed magnetic field loops falls back to the star, but the transient suspension of material within the loops leads to a statistically overdense, low velocity region around the magnetic equator, causing the spectral variations. We contrast such “dynamical magnetospheres” (DMs) with the more steady-state “centrifugal magnetospheres” of stars with rapid rotation, and discuss the prospects of using this DM paradigm to explain periodic line emission from also other non-rapidly rotating magnetic massive stars.

Spatially resolved Halpha maps and sizes of 57 strongly star-forming galaxies at z~1 from 3D-HST: evidence for rapid inside-out assembly of disk galaxies

We investigate the build-up of galaxies at z~1 using maps of Halpha and stellar continuum emission for a sample of 57 galaxies with rest-frame Halpha equivalent widths >100 Angstroms in the 3D-HST grism survey. We find that the Halpha emission broadly follows the rest-frame R-band light but that it is typically somewhat more extended and clumpy. We quantify the spatial distribution with the half-light radius. The median Halpha effective radius r_e(Halpha) is 4.2+-0.1 kpc but the sizes span a large range, from compact objects with r_e(Halpha) ~ 1.0 kpc to extended disks with r_e(Halpha) ~ 15 kpc. Comparing Halpha sizes to continuum sizes, we find =1.3+-0.1 for the full sample. That is, star formation, as traced by Halpha, typically occurs out to larger radii than the rest-frame R-band stellar continuum; galaxies are growing their radii and building up from the inside out. This effect appears to be somewhat more pronounced for the largest galaxies. Using the measured Halpha sizes, we derive star formation rate surface densities. We find that they range from ~0.05 Msun yr^{-1} kpc^{-2} for the largest galaxies to ~5 Msun yr^{-1} kpc^{-2} for the smallest galaxies, implying a large range in physical conditions in rapidly star-forming z~1 galaxies. Finally, we infer that all galaxies in the sample have very high gas mass fractions and stellar mass doubling times < 500 Myr. Although other explanations are also possible, a straightforward interpretation is that we are simultaneously witnessing the rapid formation of compact bulges and large disks at z~1.

Discovery of Halpha satellite emission in a low state of the SW Sextantis star BB Doradus

BB Dor was observed during its low state state in 2009. Signatures of both binary components are revealed in the average optical spectrum; no signature of accretion is observed. Narrow emission lines of Halpha, HeI and Na-D, as well as TiO absorption troughs trace the motion of the irradiated secondary star. We detect two additional components in the Halpha emission line that share many characteristics of similar “satellite” lines observed in the low state of magnetic cataclysmic variables of AM Her type. It is the first time such emission components are detected for an SW Sex star.

Study of LINER sources with broad H(alpha) emission. Spectral energy distribution and multiwavelength correlations

(Abridged) We attempt to infer the accretion mechanism and radiative processes giving rise to the SEDs of a well-defined optically-selected sample of LINERs showing a definite detection of broad Halpha emission (LINER 1s). We construct SEDs for six LINER~1s with simultaneous UV and X-ray fluxes, and we looked for multiwavelength, radio to X-ray and UV to X-ray, correlations. At a given X-ray luminosity, the average SED of the six LINER 1s in our sample: (1) resembles the SED of radio-loud quasars in the radio band, ~-2.7, (2) exhibits a weak UV bump, ~-1.17+-0.02 with a dispersion sigma=0.01, and (3) displays a X-ray spectrum similar to radio-quiet quasars. The bolometric luminosities inferred from the SEDs are extremely faint, at least two orders of magnitude lower than AGN. The X-ray bolometric correction, kappa_(2-10 keV), of our sample is lower than in the case of AGN, with a mean value of 16. We find a strong anticorrelation between the radio loudness parameter, R_X, and the Eddington ratio for our sample, confirming previous results. Moreover, we find a positive correlation between the radio luminosity and the X-ray luminosity which places AGN-powered LINERs, on a radio-power scale, right between low luminosity Seyferts and low luminosity radio galaxies. We complement our alpha_ox list with values derived on a well defined sample of UV-variable LINERs, and establish a strong positive correlation between alpha_ox (considering negative values) and the Eddington ratio, in contrast to the correlation found for luminous AGN. Lastly, we tested two different fundamental planes existing in the literature on our sample, in an attempt to put constraints on the debated origin of the X-ray emission, “RIAF versus jet”. The results came contradictory with one pointing toward a RIAF-dominated X-ray emission process and the other pointing toward a jet domination.

On the binary nature of the gamma-ray sources AGL J2241+4454 (=MWC 656) and HESS J0632+057 (=MWC 148) [Replacement]

We present optical spectroscopy of MWC 656 and MWC 148, the proposed optical counterparts of the gamma-ray sources AGL J2241+4454 and HESS J0632+0 57, respectively. The main parameters of the Halpha emission line (EW, FWHM and centroid velocity) in these stars are modulated on the proposed orbital periods of 60.37 and 321 days, respectively. These modulations are likely produced by the resonant interaction of the Be discs with compact stars in eccentric orbits. We also present radial velocity curves of the optical stars folded on the above periods and obtain the first orbital elements of the two gamma-ray sources thus confirming their binary nature. Our orbital solution support eccentricities e~0.4 and 0.83+-0.08 for MWC 656 and MWC 148, respectively. Further, our orbital elements imply that the X-ray outbursts in HESS J0632+057/MWC 148 are delayed ~0.3 orbital phases after periastron passage, similarly to the case of LS I +61 303. In addition, the optical photometric light curve maxima in AGL J2241+4454/MWC 656 occur ~0.25 phases passed periastron, similar to what is seen in LS I +61 303. We also find that the orbital eccentricity is correlated with orbital period for the known gamma-ray binaries. This is explained by the fact that small stellar separations are required for the efficient triggering of VHE radiation. Another correlation between the EW of Halpha and orbital period is also observed, similarly to the case of Be/X-ray binaries. These correlations are useful to provide estimates of the key orbital parameters Porb and e from the Halpha line in future Be gamma-ray binary candidates.

On the binary nature of the gamma-ray sources AGL J2241+4454 (=MWC 656) and HESS J0632+057 (=MWC 148)

We present optical spectroscopy of MWC 656 and MWC 148, the proposed optical counterparts of the gamma-ray sources AGL J2241+4454 and HESS J0632+0 57, respectively. The main parameters of the Halpha emission line (EW, FWHM and centroid velocity) in these stars are modulated on the proposed orbital periods of 60.37 and 321 days, respectively. These modulations are likely produced by the resonant interaction of the Be discs with compact stars in eccentric orbits. We also present radial velocity curves of the optical stars folded on the above periods and obtain the first orbital elements of the two gamma-ray sources thus confirming their binary nature. Our orbital solution support eccentricities e~0.4 and 0.83+-0.08 for MWC 656 and MWC 148, respectively. Further, our orbital elements imply that the X-ray outbursts in HESS J0632+057/MWC 148 are delayed ~0.3 orbital phases after periastron passage, similarly to the case of LS I +61 303. In addition, the optical photometric light curve maxima in AGL J2241+4454/MWC 656 occur ~0.25 phases passed periastron, similar to what is seen in LS I +61 303. We also find that the orbital eccentricity is correlated with orbital period for the known gamma-ray binaries. This is explained by the fact that small stellar separations are required for the efficient triggering of VHE radiation. Another correlation between the EW of Halpha and orbital period is also observed, similarly to the case of Be/X-ray binaries. These correlations are useful to provide estimates of the key orbital parameters Porb and e from the Halpha line in future Be gamma-ray binary candidates.

Observational evidence of quasar feedback quenching star formation at high redshift

Most galaxy evolutionary models require quasar feedback to regulate star formation in their host galaxies. In particular, at high redshift, models expect that feedback associated with quasar-driven outflows is so efficient that the gas in the host galaxy is largely swept away or heated up, hence suppressing star formation in massive galaxies. We observationally investigate this phenomenon by using VLT-SINFONI integral field spectroscopy of the luminous quasar 2QZJ002830.4-281706 at z=2.4. The spectra sample the optical emission lines redshifted into the near-IR. The [OIII]5007 emission line kinematics map reveals a massive outflow on scales of several kpc. The detection of narrow Halpha emission reveals star formation in the quasar host galaxy, with SFR \sim 100 Msun/yr. However, the star formation is not distributed uniformly, it is strongly suppressed in the region with the highest outflow velocity and highest velocity dispersion. This result indicates that in this region star formation is strongly quenched by the quasar outflow, which is cleaning the galaxy disk of its molecular gas. This is one of the first direct observational evidence of quasar feedback quenching star formation at high redshift.

Observational evidence of quasar feedback quenching star formation at high redshift [Replacement]

Most galaxy evolutionary models require quasar feedback to regulate star formation in their host galaxies. In particular, at high redshift, models expect that feedback associated with quasar-driven outflows is so efficient that the gas in the host galaxy is largely swept away or heated up, hence suppressing star formation in massive galaxies. We observationally investigate this phenomenon by using VLT-SINFONI integral field spectroscopy of the luminous quasar 2QZJ002830.4-281706 at z=2.4. The spectra sample the optical emission lines redshifted into the near-IR. The [OIII]5007 emission-line kinematics map reveals a massive outflow on scales of several kpc. The detection of narrow Halpha emission reveals star formation in the quasar host galaxy, with SFR=100 Msun/yr. However, the star formation is not distributed uniformly, but is strongly suppressed in the region with the highest outflow velocity and highest velocity dispersion. This result indicates that star formation in this region is strongly quenched by the quasar outflow, which is cleaning the galaxy disk of its molecular gas. This is one of the first direct observational proofs of quasar feedback quenching the star formation at high redshift.

Spectral Energy Distributions of a set of HII regions in M33 (HerM33es)

Within the framework of the HerM33es Key Project for Herschel and in combination with multi-wavelength data, we study the Spectral Energy Distribution (SED) of a set of HII regions in the Local Group Galaxy M33. Using the Halpha emission, we perform a classification of a selected HII region sample in terms of morphology, separating the objects in filled, mixed, shell and clear shell objects. We obtain the SED for each HII region as well as a representative SED for each class of objects. We also study the emission distribution of each band within the regions. We find different trends in the SEDs for each morphological type that are related to properties of the dust and their associated stellar cluster. The emission distribution of each band within the region is different for each morphological type of object.

Post-common envelope binaries from SDSS - XIV. The DR7 white dwarf-main sequence binary catalogue

We present an updated version of the spectroscopic white dwarf-main sequence (WDMS) binary catalogue from the Sloan Digital Sky Survey (SDSS). 395 new systems are serendipitous discoveries from the spectroscopic SDSSI/II Legacy targets. As part of SEGUE, we have carried out a dedicated and efficient (64 per cent success rate) search for WDMS binaries with a strong contribution of the companion star, which were underrepresented by all previous surveys, identifying 251 additional systems. In total, our catalogue contains 2248 WDMS binaries, and includes, where available, magnitudes from the GALEX All Sky Survey in the ultraviolet and from the UKIRT Infrared Sky Survey (UKIDSS) in the near-infrared. We also provide radial velocities of the companion stars, measured from the SDSS spectroscopy using the NaI8183.27,8194.81 absorption doublet and/or the Halpha emission. Using an updated version of our spectral decomposition/fitting technique we determine/update the white dwarf effective temperatures, surface gravities and masses, as well as the spectral type of the companion stars for the entire catalogue. Comparing the distributions of white dwarf mass, temperature, and companion spectral type, we confirm that our SEGUE survey project has been successful in identifying WDMS binaries with cooler and more massive white dwarfs, as well as earlier spectral types than found previously. Finally, we have developed a publicly available interactive on-line data base for spectroscopic SDSS WDMS binaries containing all available stellar parameters, radial velocities and magnitudes which we briefly describe.

Long-term magnetic field monitoring of the Sun-like star Ksi Boo A

Aims. We aim at investigating the long-term temporal evolution of the magnetic field of the solar-type star Ksi Boo A, both from direct magnetic field measurements and from the simultaneous estimate of indirect activity indicators. Methods. We use 7 time-series of high-resolution, circularly-polarized spectra obtained with the NARVAL spectropolarimeter between 2007 and 2011, for a total of 76 spectra. Using about 6,100 photospheric spectral lines covering the visible domain, we employ a cross-correlation procedure to compute, from each spectrum, a mean polarized line profile. We model the large-scale photospheric magnetic field of the star by means of Zeeman-Doppler Imaging and follow the year-to-year evolution of the reconstructed magnetic topology. Simultaneously, we monitor the width of several magnetically-sensitive spectral lines, the radial velocity and line asymmetry of intensity line profiles and the chromospheric emission in the cores of the Ca II H and Halpha lines. Results. During the highest observed activity states, in 2007 and 2011, the large-scale field is almost axisymmetric and is strongly dominated by its toroidal component. This component persists with a constant polarity and carrying a significant fraction of the magnetic energy of the large-scale surface field at all observing epochs. The magnetic topologies reconstructed for these activity maxima are very similar, suggesting a form of short cyclicity in the large-scale field distribution. Correlated temporal evolutions, due to both rotational modulation and seasonal variability, are observed between the Ca II emission, the Halpha emission and the width of magnetically-sensitive lines. Whenever available, differential rotation measurements reveal a strong latitudinal shear in excess of 0.2 rad/d.

 

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