Posts Tagged galactic disk

Recent Postings from galactic disk

Bending and Breathing Modes of the Galactic Disk

We explore the hypothesis that a passing satellite or dark matter subhalo has excited coherent oscillations of the Milky Way’s stellar disk in the direction perpendicular to the Galactic midplane. This work is motivated by recent observations of spatially dependent bulk vertical motions within ~ kpc of the Sun. A satellite can transfer a fraction of its orbital energy to the disk stars as it plunges through the Galactic midplane thereby heating and thickening the disk. Bulk motions arise during the early stages of such an event when the disk is still in an unrelaxed state. We present simple toy-model calculations and simulations of disk-satellite interactions, which show that the response of the disk depends on the relative velocity of the satellite. When the component of the satellite’s velocity perpendicular to the disk is small compared with that of the stars, the perturbation is predominantly a bending mode. Conversely, breathing and higher order modes are excited when the vertical velocity of the satellite is larger than that of the stars. We argue that the compression and rarefaction motions seen in three different surveys are in fact breathing mode perturbations of the Galactic disk.

The scale height of gas traced by [CII] in the Galactic plane

The distribution of various interstellar gas components and the pressure in the interstellar medium (ISM) is a result of the interplay of different dynamical mechanisms and energy sources on the gas in the Milky Way. The scale heights of the different gas tracers, such as HI and CO, are a measure of these processes. The scale height of [CII] emission in the Galactic plane is important for understanding those ISM components not traced by CO or HI. We determine the average distribution of [CII] perpendicular to the plane in the inner Galactic disk and compare it to the distributions of other key gas tracers, such as CO and HI. We calculated the vertical, z, distribution of [CII] in the inner Galactic disk by adopting a model for the emission that combines the latitudinal, b, spectrally unresolved BICE survey, with the spectrally resolved $Herschel$ Galactic plane survey of [CII] at b = 0 deg. Our model assumed a Gaussian emissivity distribution vertical to the plane, and related the distribution in z to that of the latitude b using the spectrally resolved [CII] Herschel survey as the boundary solution for the emissivity at b=0 deg. We find that the distribution of [CII] perpendicular to the plane has a full-width half-maximum of 172 pc, larger than that of CO, which averages ~110 pc in the inner Galaxy, but smaller than that of HI, ~230 pc, and is offset by -28 pc. We explain the difference in distributions of [CII], CO, and HI as due to [CII] tracing a mix of ISM components. Models of hydrostatic equilibrium of clouds in the disk predict different scale heights, for the same interstellar pressure. The diffuse molecular clouds with [CII] but no CO emission likely have a scale height intermediate between the low density atomic hydrogen HI clouds and the dense CO molecular clouds.

Widespread Rotationally-Hot Hydronium Ion in the Galactic Interstellar Medium

We present new observations of the (6,6) and (9,9) inversion transitions of the hydronium ion toward Sagittarius B2(N) and W31C. Sensitive observations toward Sagittarius B2(N) show that the high, ~ 500 K, rotational temperatures characterizing the population of the highly-excited metastable H3O+ rotational levels are present over a wide range of velocities corresponding to the Sagittarius B2 envelope, as well as the foreground gas clouds between the Sun and the source. Observations of the same lines toward W31C, a line of sight that does not intersect the Central Molecular Zone, but instead traces quiescent gas in the Galactic disk, also imply a high rotational temperature of ~ 380 K, well in excess of the kinetic temperature of the diffuse Galactic interstellar medium. While it is plausible that some fraction of the molecular gas may be heated to such high temperatures in the active environment of the Galactic center, characterized by high X-ray and cosmic ray fluxes, shocks and high degree of turbulence, this is unlikely in the largely quiescent environment of the Galactic disk clouds. We suggest instead that the highly-excited states of the hydronium ion are populated mainly by exoergic chemical formation processes and temperature describing the rotational level population does not represent the physical temperature of the medium. The same arguments may be applicable to other symmetric top rotors, such as ammonia. This offers a simple explanation to the long-standing puzzle of the presence of a pervasive, hot molecular gas component in the central region of the Milky Way. Moreover, our observations suggest that this is a universal process, not limited to the active environments associated with galactic nuclei.

The Galactic bar and the large scale velocity gradients in the Galactic disk

We investigate whether the cylindrical (galactocentric) radial velocity gradient of ~ -3 km/sec/kpc, directed radially from the Galactic center and recently observed in the stars of the Solar Neighborhood with the RAVE survey, can be explained by the resonant effects of the bar near the Solar Neighborhood. We compare the results of test particle simulations of the Milky Way with a potential including a rotating bar with observations from the RAVE survey. To this end we apply the RAVE selection function to the simulations, and convolve these with the characteristic RAVE errors. We explore different "solar neighborhoods" in the simulations as well as different bar models. We find that the bar induces a negative radial velocity gradient at every height from the Galactic plane, outside the Outer Lindblad Resonance, and for angles from the long axis of the bar compatible with the current estimates. The selection function and errors do not wash away the gradient, but often make it steeper, especially near the Galactic plane because this is where the RAVE survey is less radially extended. No gradient in the vertical velocity is present in our simulations, from which we may conclude that this cannot be induced by the bar.

The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk

We study the relationship between age, metallicity, and alpha-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters (including non-LTE), and the survey selection effects, which are caused by observing the stars in a given photometric box. We find that the colour and magnitude cuts on the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as large as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages (0.5 to 13.5 Gyr), Galacto-centric distances from $6$ to 9.5 kpc and vertical distances above the plane 0 < |Z| < 1.5 kpc.In the context of Galaxy formation, we find that: i) the observed age-metallicity relation is nearly flat in the range of ages between 0 and 8 Gyr, ii) there is a decline in [Fe/H] for stars with ages above 9 Gyr, which is where we detect no metal-rich stars at all; this cannot be explained by the survey selection functions, iii) there is a significant scatter of [Fe/H] at any age. In agreement with earlier work in the literature, we find that radial abundance gradients change as a function of vertical distance above the plane. The Mg gradient steepens and becomes negative. There is a well-defined double-branching of Mg abundances for stars at |Z| > 300 pc above the plane: the low and high alpha-components partly overlapping in age. The dispersion of [Mg/Fe] abundances is significant at any age. In particular, the stars with ages above 9 Gyr show a broad range in both [Mg/Fe], from 0 to 0.4 dex, and metallicity, from solar to [Fe/H] ~ -1.

The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk [Replacement]

We study the relationship between age, metallicity, and alpha-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters and the selection effects that are caused by the photometric target preselection. We find that the colour and magnitude cuts in the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as large as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages (0.5 to 13.5 Gyr), Galacto-centric distances from 6 to 9.5 kpc and vertical distances from the plane 0 < |Z| < 1.5 kpc. On this basis, we find that: i) the observed age-metallicity relation is nearly flat in the range of ages between 0 and 8 Gyr, ii) at ages older than 9 Gyr, we see a decrease in [Fe/H] and a clear absence of metal-rich stars; this cannot be explained by the survey selection functions, iii) there is a significant scatter of [Fe/H] at any age, iv) [Mg/Fe] increases with age, but the dispersion of [Mg/Fe] at ages > 9 Gyr is not as small as advocated by some other studies. In agreement with earlier work, we find that radial abundance gradients change as a function of vertical distance from the plane. The [Mg/Fe] gradient steepens and become negative. We also show that the inner disk is not only more alpha-rich compared to the outer disk, but also older, as traced independently by the ages and Mg abundances of stars.

The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk [Replacement]

We study the relationship between age, metallicity, and alpha-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters and the selection effects that are caused by the photometric target preselection. We find that the colour and magnitude cuts in the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as high as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages from 0.5 Gyr to 13.5 Gyr, Galactocentric distances from 6 kpc to 9.5 kpc, and vertical distances from the plane 0 < |Z| < 1.5 kpc. On this basis, we find that i) the observed age-metallicity relation is nearly flat in the range of ages between 0 Gyr and 8 Gyr; ii) at ages older than 9 Gyr, we see a decrease in [Fe/H] and a clear absence of metal-rich stars; this cannot be explained by the survey selection functions; iii) there is a significant scatter of [Fe/H] at any age; and iv) [Mg/Fe] increases with age, but the dispersion of [Mg/Fe] at ages > 9 Gyr is not as small as advocated by some other studies. In agreement with earlier work, we find that radial abundance gradients change as a function of vertical distance from the plane. The [Mg/Fe] gradient steepens and becomes negative. In addition, we show that the inner disk is not only more alpha-rich compared to the outer disk, but also older, as traced independently by the ages and Mg abundances of stars.

The Gaia-ESO Survey: Abundance ratios in the inner-disk open clusters Trumpler 20, NGC 4815, NGC 6705

Open clusters are key tools to study the spatial distribution of abundances in the disk and their evolution with time. Using the first release of stellar parameters and abundances of the Gaia-ESO Survey, we analyse the chemical properties of stars in three old/intermediate-age open clusters, namely NGC 6705, NGC 4815, and Trumpler 20, all located in the inner part of the Galactic disk at Galactocentric radius R$_{GC}\sim$7 kpc, aiming at proving their homogeneity and at comparing them with the field population. We study the abundance ratios of elements belonging to two different nucleosynthetic channels: $\alpha$-elements and iron-peak elements. The main results can be summarised as follows: i) cluster members are chemically homogeneous within 3-$\sigma$ in all analysed elements; ii) the three clusters have comparable [El/Fe] patters within $\sim$1-$\sigma$, but they differ in their global metal content [El/H], with NGC 4815 having the lowest metallicity. Their [El/Fe] ratios show differences and analogies with those of the field population, both in the solar neighbourhood and in the bulge/inner disk; iii) comparing the abundance ratios with the results of two chemical evolution models and with field star abundance distributions, we find that the abundance ratios of Mg, Ni, Ca in NGC 6705 might require an inner birthplace, implying a subsequent variation of its R$_{GC}$ during its lifetime, consistent with previous orbit determination. The full dataset of the Gaia-ESO Survey will be a superlative tool to constrain the chemical evolution of our Galaxy by disentangling different formation and evolution scenarios.

The WISE Catalog of Galactic HII Regions

Using data from the all-sky Wide-Field Infrared Survey Explorer (WISE) satellite, we made a catalog of over 8000 Galactic HII regions and HII region candidates by searching for their characteristic mid-infrared (MIR) morphology. WISE has sufficient sensitivity to detect the MIR emission from HII regions located anywhere in the Galactic disk. We believe this is the most complete catalog yet of regions forming massive stars in the Milky Way. Of the ~8000 cataloged sources, ~1500 have measured radio recombination line (RRL) or H$\alpha$ emission, and are thus known to be HII regions. This sample improves on previous efforts by resolving HII region complexes into multiple sources and by removing duplicate entries. There are ~2500 candidate HII regions in the catalog that are spatially coincident with radio continuum emission. Our group’s previous RRL studies show that ~95% of such targets are HII regions. We find that ~500 of these candidates are also positionally associated with known HII region complexes, so the probability of their being bona fide HII regions is even higher. At the sensitivity limits of existing surveys, ~4000 catalog sources show no radio continuum emission. Using data from the literature, we find distances for ~1500 catalog sources, and molecular velocities for ~1500 HII region candidates.

On the alignment of PNe and local magnetic field at the galactic centre: MHD numerical simulations

For the past decade observations of the alignement of PNe symmetries with respect to the galactic disk have led to conflicting results. Recently observational evidence for alignment between PNe and local interstellar magnetic fields in the central part of the Galaxy ($b < 5^\circ$) has been found. We studied the role of the interstellar magnetic field on the dynamical evolution of a PN by means of an analytical model and from 3D MHD numerical simulations. We test under what conditions typical ejecta would have their dynamics severely modified by an interstellar magnetic field. We found that uniform fields of $> 100\mu$G are required in order to be dynamically dominant. This is found to occur only at later evolutionary stages, therefore being unable to change the general morphology of the nebula. However, the symmetry axis of bipolar and elliptical nebulae end up aligned to the external field. This result can explain why different samples of PNe result in different conclusions regarding the alignment of PNe. Objects located at high galactic latitudes, or at large radii, should present no preferential alignment with respect to the galactic plane. PNe located at the galactic centre and low latitudes would, on the other hand, be preferentiably aligned to the disk. Finally, we present synthetic polarization maps of the nebulae to show that the polarization vectors, as well as the field lines at the expanding shell, are not uniform even in the strongly magnetized case, indicating that polarization maps of nebulae are not adequate in probing the orientation, or intensity, of the dominant external field.

Large Variety of New Pulsating Stars in the OGLE-III Galactic Disk Fields [Replacement]

We present the results of a search for pulsating stars in the 7.12 deg^2 OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 31 Long-Period Variables, such as Miras and Semi-Regular Variables, one pulsating white dwarf, and 58 very likely delta Sct type stars. Based on asteroseismic models constructed for one quadruple-mode and six triple-mode delta Sct type pulsators, we estimated masses, metallicities, ages, and distance moduli to these objects. The modeled stars have masses in the range 0.9-2.5 M_sun and are located at distances between 2.5 kpc and 6.2 kpc. Two triple-mode and one double-mode pulsators seem to be Population II stars of the SX Phe type, probably from the Galactic halo. Our sample also includes candidates for Type II Cepheids and unclassified short-period (P<0.23 d) multi-mode stars which could be either delta Sct or beta Cep type stars. One of the detected variables is a very likely delta Sct star with an exceptionally high peak-to-peak I-band amplitude of 0.35 mag at the very short period of 0.0196 d. All reported pulsating variables but one object are new discoveries. They are included in the OGLE-III Catalog of Variable Stars. Finally, we introduce the on-going OGLE-IV Galactic Disk Survey, which covers more than half of the Galactic plane. For the purposes of future works on the spiral structure and star formation history of the Milky Way, we have already compiled a list of known Galactic Classical Cepheids.

Large Variety of New Pulsating Stars in the OGLE-III Galactic Disk Fields

We present the results of a search for pulsating stars in the 7.12 deg^2 OGLE-III Galactic disk area in the direction tangent to the Centaurus Arm. We report the identification of 20 Classical Cepheids, 45 RR Lyr type stars, 14 Long-Period Variables, such as Miras and Semi-Regular Variables, and 56 very likely delta Sct type stars. Based on asteroseismic models constructed for one quadruple-mode and six triple-mode delta Sct type pulsators, we estimated masses, metallicities, ages, and distance moduli to these objects. The modeled stars have masses in the range 0.9-2.5 M_sun and are located at distances between 2.5 kpc and 6.2 kpc. Two triple-mode and one double-mode pulsators seem to be Population II stars of the SX Phe type, probably from the Galactic halo. All reported pulsating variables but one object are new discoveries. They are included in the OGLE-III Catalog of Variable Stars. Finally, we introduce the on-going OGLE-IV Galactic Disk Survey, which covers half of the Galactic plane. For the purposes of future works on the spiral structure and star formation history of the Milky Way, we have already compiled a list of known Galactic Classical Cepheids.

Analyzing spiral structure in a galactic disk with a gaseous component

Using GADGET2, we performed an SPH+N-body simulation of a galactic disk with stellar and gas particles. This simulation allows to compare the spiral structure in the different disk components. Also, we performed a simulation without gaseous component to explore the effects of the gas in the spiral pattern of the stars.

Thermals in stratified regions of the ISM

We present a model of a "thermal" (i.e., a hot bubble) rising within an exponentially stratified region of the ISM. This model includes terms representing the ram pressure braking and the entrainment of environmental gas into the thermal. We then calibrate the free parameters associated with these two terms through a comparison with 3D numerical simulations of a rising bubble. Finally, we apply our "thermal" model to the case of a hot bubble produced by a SN within the stratified ISM of the Galactic disk.

A couple of recent developments in the structure of the outer disk of the Milky Way

In this contribution we summarize recent achievements by our group on the understanding of the structure of the outer Galactic disk, with particular emphasis to the outer disk extent, and the spiral structure beyond the solar circle.

Extreme Galaxies During Reionization: Testing ISM and Disk Models

We test the ability of equilibrium galactic disk and one-zone interstellar medium models to describe the physical and emission properties of a sample of quasar hosts, submillimeter galaxies, and Lyman-alpha emitters during the epoch of cosmic reionization at z>~6. We find that the size, line widths, star formation rates, black hole accretion rates, gas masses and temperatures, and the relationships between these properties are all well-described by our model. In particular, the quasars in our sample are hosted by halos with masses of roughly 10^12–10^13 M_sun and require an inflow velocity of gas toward the disk center of v_in=sqrt(2) beta sigma with beta~0.1—somewhat higher if quasar outflows are significant—where sigma is the halo velocity dispersion. We also provide approximate fitting formulae to our results for comparison with future observations. However, our fiducial model underestimates the [CII] line emission from the systems in our sample by an order of magnitude or more. We explore two variants to our model and find that the requisite flux can be produced if either the star formation efficiency of molecular clouds is higher or the depletion of metals onto dust at fixed metallicity is lower at higher redshift than expected from standard models. Our models also predict a higher median density in molecular clouds than found in fits to observations resulting from turbulent fragmentation in molecular clouds leading to a more thermalized CO(6-5) line and a higher CO(6-5)/CO(1-0) ratio than determined observationally. While we leave this last issue unresolved in detail, we suggest that either clouds smaller than the local Jeans mass or a support mechanism other than turbulence could result in a lower turbulent Mach number and more subthermal CO(6-5) emission.

Star Formation Sites toward the Galactic Center Region: The Correlation of CH3OH Masers, H2O Masers, and Near-IR Green Sources

We present a study of star formation in the Central Molecular Zone (CMZ) of our Galaxy through the association of three star formation indicators: 6.7 GHz CH3OH masers, 22 GHz H2O masers, and enhanced 4.5 micron emission (`green’) sources. We explore how star formation in the Galactic center (l < 1.3 deg, |b| < 10′, where l and b are Galactic longitude and Galactic latitude) compares with that of the Galactic disk (6 deg < l < 345 deg, |b| < 2 deg). Using an automated algorithm, we search for enhanced 4.5 micron emission sources toward 6.7 GHz CH3OH masers detected in the Parkes Methanol Multibeam Survey. We combine these results with our 22 GHz H2O maser survey of the CMZ carried out with the Mopra telescope. We find that the correlation of CH3OH masers with green sources is a function of Galactic latitude, with a minimum close to b=0 and increasing with |b| (toward the central part of the Galaxy, 6 deg < l < 345 deg, |b| < 2 deg). We find no significant difference between the correlation rate of CH3OH masers with green sources in the CMZ and the disk. This suggests that although the physical conditions of the gas are different in the Galactic center from that of the Galactic disk, once gravitational instability sets in at sufficiently high densities, signatures of star formation appear to be similar in both regions. Moreover, the detection of green sources, even at the distance of the Galactic center, shows that our technique can easily identify the early stages of star formation, especially in low extinction regions of the Galaxy. Through the association of H2O and CH3OH masers, we identify 15 star-forming sites in the CMZ. We find no coincident H2O and CH3OH masers outside the CMZ (with limited H2O maser survey coverage outside the CMZ), possibly indicating a difference in the maser evolutionary sequence for star-forming cores in the Galactic center region and the disk.

Substructure in bulk velocities of Milky Way disk stars

We find that Galactic disk stars near the anticenter exhibit velocity asymmetries in both the Galactocentric radial and vertical components across the mid-plane as well as azimuthally. These findings are based on LAMOST spectroscopic velocities for a sample of ~400,000 F-type stars, combined with proper motions from the PPMXL catalog for which we have derived corrections to the zero points based in part on spectroscopically discovered galaxies and QSOs from LAMOST. In the region within 2 kpc outside the Sun’s radius and +/-2 kpc from the Galactic midplane, we show that stars above the plane exhibit net outward radial motions with downward vertical velocities, while stars below the plane have roughly the opposite behavior. We discuss this in the context of other recent findings, and conclude that we are likely seeing the signature of vertical disturbances to the disk due to an external perturbation.

Exploring the Milky Way stellar disk. A detailed elemental abundance study of 703 F and G dwarf stars in the Solar neighbourhood

AIMS: The aim of this paper is to explore and map the age and abundance structure of the stars in the nearby Galactic disk. Methods: We have conducted a high-resolution spectroscopic study of 703 F and G dwarf stars in the Solar neighbourhood. The star sample has been kinematically selected to trace the Galactic thin and thick disks to their extremes, the metal-rich stellar halo, sub-structures in velocity space such as the Hercules stream and the Arcturus moving group, as well as stars that cannot (kinematically) be associated with either the thin disk or the thick disk. The determination of stellar parameters and elemental abundances is based on a standard 1-D LTE analysis using equivalent width measurements in high-resolution (R=40000-110000) and high signal-to-noise (S/N=150-300) spectra obtained with FEROS, SOFIN, UVES, and MIKE. NLTE corrections for individual Fe I lines were employed in every step of the analysis. Results: We present stellar parameters, stellar ages, kinematical parameters, orbital parameters, and detailed elemental abundances for O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, and Ba for 703 nearby F and G dwarf stars. Our data show there is an old and alpha-enhanced disk population, and then a younger and less alpha-enhanced disk population. While they greatly overlap in metallicity between -0.7<[Fe/H]<+0.1 they show a bimodal distribution in [alpha/Fe]. This bimodality becomes even clearer if stars that are more susceptible to uncertainties and NLTE effects are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between different stellar populations are to be revealed. We furthermore find that the alpha-enhanced population have orbital parameters placing their birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk, abridged…

Exploring the Milky Way stellar disk. A detailed elemental abundance study of 714 F and G dwarf stars in the Solar neighbourhood [Replacement]

ABRIDGED: METHODS: We have conducted a high-resolution spectroscopic study of 714 F and G dwarf and subgiant stars in the Solar neighbourhood. The star sample has been kinematically selected to trace the Galactic thin and thick disks to their extremes…… The determination of stellar parameters and elemental abundances is based on a standard 1-D LTE analysis using equivalent width measurements in high-resolution (R=40000-110000) and high signal-to-noise (S/N=150-300) spectra obtained with….. RESULTS: …. Our data show that there is an old and alpha-enhanced disk population, and a younger and less alpha-enhanced disk population. While they overlap greatly in metallicity between -0.7<[Fe/H]<+0.1, they show a bimodal distribution in [alpha/Fe]. This bimodality becomes even clearer if stars where stellar parameters and abundances show larger uncertainties (Teff<5400 K) are discarded, showing that it is important to constrain the data set to a narrow range in the stellar parameters if small differences between stellar populations are to be revealed. We furthermore find that the alpha-enhanced population has orbital parameters placing the stellar birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk……….. We furthermore have discovered that a standard 1-D, LTE analysis, utilising ionisation and excitation balance of Fe I and Fe II lines produces a flat lower main sequence. As the exact cause for this effect is unclear we chose to apply an empirical correction. Turn-off, and more evolved, stars, appears to be un-affected.

Nitrogen Abundances and the Distance Moduli of the Pleiades and Hyades

Recent reanalyses of HIPPARCOS parallax data confirm a previously noted discrepancy with the Pleiades distance modulus estimated from main-sequence fitting in the color-magnitude diagram. One proposed explanation of this distance modulus discrepancy is a Pleiades He abundance that is significantly larger than the Hyades value. We suggest that, based on our theoretical and observational understanding of Galactic chemical evolution, nitrogen abundances may serve as a proxy for helium abundances of disk stars. Utilizing high-resolution near-UV Keck/HIRES spectroscopy, we determine N abundances in the Pleiades and Hyades dwarfs from NH features in the 3330 Ang region. While our Hyades N abundances show a modest 0.2 dex trend over a 800 K Teff range, we find the Pleiades N abundance (by number) is 0.13+/-0.05 dex lower than in the Hyades for stars in a smaller overlapping Teff range around 6000 K; possible systematic errors in the lower Pleiades N abundance result are estimated to be at the <0.10 dex level. Our results indicate [N/Fe]=0 for both the Pleiades and Hyades, consistent with the ratios exhibited by local Galactic disk field stars in other studies. If N production is a reliable tracer of He production in the disk, then our results suggest the Pleiades He abundance is no larger than that in the Hyades. This finding is supported by the relative Pleiades-Hyades C, O, and Fe abundances interpreted in the current context of Galactic chemical evolution, and is resistant to the effects on our derived N abundances of a He abundance difference like that needed to explain the Pleiades distance modulus discrepancy. A physical explanation of the Pleiades distance modulus discrepancy does not appear to be related to He abundance.

A direct dynamical measurement of the Milky Way's disk surface density profile, disk scale length, and dark matter profile at 4 kpc < R < 9 kpc

We present and apply rigorous dynamical modeling with which we infer unprecedented constraints on the stellar and dark matter mass distribution within our Milky Way (MW), based on large sets of phase-space data on individual stars. Specifically, we model the dynamics of 16,269 G-type dwarfs from SEGUE, which sample 5 < R/kpc < 12 and 0.3 < |Z|/kpc < 3. We independently fit a parameterized MW potential and a three-integral, action-based distribution function (DF) to the phase-space data of 43 separate abundance-selected sub-populations (MAPs), accounting for the complex selection effects affecting the data. We robustly measure the total surface density within 1.1 kpc of the mid-plane to about 5% over the range 4.5< R/kpc < 9. Using metal-poor MAPs with small radial scale lengths as dynamical tracers probes 4.5 < R/kpc < 7, while MAPs with longer radial scale lengths sample 7 < R/kpc < 9. We measure the mass-weighted Galactic disk scale length to be R_d = 2.15+/-0.14 kpc, in agreement with the photometrically inferred spatial distribution of stellar mass. We thereby measure dynamically the mass of the Galactic stellar disk to unprecedented accuracy: M_* = 4.6+/-0.3×10^{10} Msun and a total local surface density of \Sigma_{R_0}(Z=1.1 kpc) = 68+/-4 Msun/pc^2 of which 38+/-4 Msun/pc^2 is contributed by stars and stellar remnants. By combining our surface density measurements with data on the terminal velocity curve, we find that the MW’s disk is maximal in the sense that V_{c,disk} / V_{c,total} = 0.83+/-0.04 at R=2.2R_d. We also constrain for the first time the radial profile of the dark halo at such small Galactocentric radii, finding that \rho_{DM}(r) ~ 1 / r^\alpha with \alpha < 1.53 at 95% confidence. Our results show that action-based distribution-function modeling of complex stellar data sets is now a feasible approach that will be fruitful for interpreting Gaia data.

Minimum Distance Estimation of Milky Way Model Parameters and Related Inference [Cross-Listing]

We propose a method to estimate the location of the Sun in the disk of the Milky Way using a method based on the Hellinger distance and construct confidence sets on our estimate of the unknown location using a bootstrap based method. Assuming the Galactic disk to be two-dimensional, the sought solar location then reduces to the radial distance separating the Sun from the Galactic center and the angular separation of the Galactic center to Sun line, from a pre-fixed line on the disk. On astronomical scales, the unknown solar location is equivalent to the location of us earthlings who observe the velocities of a sample of stars in the neighborhood of the Sun. This unknown location is estimated by undertaking pairwise comparisons of the estimated density of the observed set of velocities of the sampled stars, with densities estimated using synthetic stellar velocity data sets generated at chosen locations in the Milky Way disk according to four base astrophysical models. The "match" between the pair of estimated densities is parameterized by the affinity measure based on the familiar Hellinger distance. We perform a novel cross-validation procedure to establish a desirable "consistency" property of the proposed method.

A hot Jupiter transiting a mid-K dwarf found in the pre-OmegaCam Transit Survey

We describe the pre-OmegaTranS project, a deep survey for transiting extra-solar planets in the Carina region of the Galactic Disk. In 2006-2008 we observed a single dense stellar field with a very high cadence of ~2min using the ESO Wide Field Imager at the La Silla Observatory. Using the Astronomical Wide-field System for Europe and the Munich Difference Imaging Analysis pipeline, a module that has been developed for this project, we created the light curves of 16000 stars with more than 4000 data points which we searched for periodic transit signals using a box-fitting least-squares detection algorithm. All light curves are publicly available. In the course of the pre-OmegaTranS project we identified two planet candidates – POTS-1b and POTS-C2b – which we present in this work. With extensive follow-up observations we were able to confirm one of them, POTS-1b, a hot Jupiter transiting a mid-K dwarf. The planet has a mass of 2.31+-0.77M_Jup and a radius of 0.94+-0.04R_Jup and a period of P=3.16d. The host star POTS-1 has a radius of 0.59+-0.02R_Sun and a mass of 0.70+-0.05M_Sun. Due to its low apparent brightness of I=16.1mag the follow-up and confirmation of POTS-1b was particularly challenging and costly.

Search for hidden turbulent gas through interstellar scintillation

Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected when the light of remote stars crosses a Galactic – disk or halo – refractive medium such as a molecular cloud. We present the promising results of a test performed with the ESO-NTT and the perspectives of detection.

A Low Metallicity Molecular Cloud In The Lower Galactic Halo

We find evidence for the impact of infalling, low-metallicity gas on the Galactic disk. This is based on FUV absorption line spectra, 21-cm emission line spectra, and FIR mapping to estimate the abundance and physical properties of IV21 (IVC135+54-45), a galactic intermediate-velocity molecular cloud (IVMC) that lies ~300 pc above the disk. The metallicity of IV21 was estimated using observations toward the sdB star PG1144+615, located at a projected distance of 16 pc from the cloud’s densest core, by measuring ion and HI column densities for comparison with known solar abundances. Despite the cloud’s bright FIR emission and large column densities of molecular gas as traced by CO, we find that it has a sub-solar metallicity of log(Z/Z_Sun)=-0.43 +/- 0.12dex. IV21 is thus the first known sub-solar metallicity cloud in the solar neighborhood. In contrast, most intermediate-velocity clouds (IVC) have near-solar metallicities and are believed to originate in the Galactic Fountain. The cloud’s low metallicity is also atypical for Galactic molecular clouds, especially in the light of the bright FIR emission which suggest a substantial dust content. The measured I_100mu/N(HI) ratio is a factor of three below the average found in high latitude \HI clouds within the solar neighborhood. We argue that IV21 represents the impact of an infalling, low-metallicity high-velocity cloud (HVC) that is mixing with disk gas in the lower Galactic halo.

Global survey of star clusters in the Milky Way II. The catalogue of basic parameters

Although they are the main constituents of the Galactic disk population, for half of the open clusters in the Milky Way reported in the literature nothing is known except the raw position and an approximate size. The main goal of this study is to determine a full set of uniform spatial, structural, kinematic, and astrophysical parameters for as many known open clusters as possible. On the basis of stellar data from PPMXL and 2MASS, we used a dedicated data-processing pipeline to determine kinematic and photometric membership probabilities for stars in a cluster region. For an input list of 3784 targets from the literature, we confirm that 3006 are real objects, the vast majority of them are open clusters, but associations and globular clusters are also present. For each confirmed object we determined the exact position of the cluster centre, the apparent size, proper motion, distance, colour excess, and age. For about 1500 clusters, these basic astrophysical parameters have been determined for the first time. For the bulk of the clusters we also derived the tidal radius. We estimated additionally average radial velocities for more than 30% of the confirmed clusters. The present sample (called MWSC) reaches both the central parts of the Milky Way and its outer regions. It is almost complete up to 1.8 kpc from the Sun and also covers neighbouring spiral arms. However, for a small subset of the oldest open clusters ($\log t \gtrsim 9$) we found some evidence of incompleteness within about 1 kpc from the Sun.

The Open Cluster Chemical Analysis and Mapping Survey: Local Galactic Metallicity Gradient with APOGEE using SDSS DR10

The Open Cluster Chemical Analysis and Mapping (OCCAM) Survey aims to produce a comprehensive, uniform, infrared-based dataset for hundreds of open clusters, and constrain key Galactic dynamical and chemical parameters from this sample. This first contribution from the OCCAM survey presents analysis of 141 members stars in 28 open clusters with high-resolution metallicities derived from a large uniform sample collected as part of the SDSS-III/Apache Point Observatory Galactic Evolution Experiment (APOGEE). This sample includes the first high-resolution metallicity measurements for 22 open clusters. With this largest ever uniformly observed sample of open cluster stars we investigate the Galactic disk gradients of both [M/H] and [alpha/M]. We find basically no gradient across this range in [alpha/M], but [M/H] does show a gradient for R_{GC} < 10 kpc and a significant flattening beyond R_{GC} = 10 kpc. In particular, whereas fitting a single linear trend yields an [M/H] gradient of -0.09 +/- 0.03$ dex/kpc — similar to previously measure gradients inside 13 kpc — by independently fitting inside and outside 10 kpc separately we find a significantly steeper gradient near the Sun (7.9 <= R_{GC} <= 10) than previously found (-0.20 +/- 0.08 dex/kpc) and a nearly flat trend beyond 10 kpc (-0.02 +/- 0.09 dex/kpc).

The Origin of HVS17, an Unbound Main Sequence B Star at 50 kpc

We analyze Keck ESI spectroscopy of HVS17, a B-type star traveling with a Galactic rest frame radial velocity of +445 km/s in the outer halo of the Milky Way. HVS17 has the projected rotation of a main sequence B star and is chemically peculiar, with solar iron abundance and sub-solar alpha abundance. Comparing measured T_eff and logg with stellar evolution tracks implies that HVS17 is a 3.91 +-0.09 Msun, 153 +-9 Myr old star at a Galactocentric distance of r=48.5 +-4.6 kpc. The time between its formation and ejection significantly exceeds 10 Myr and thus is difficult to reconcile with any Galactic disk runaway scenario involving massive stars. The observations are consistent, on the other hand, with a hypervelocity star ejection from the Galactic center. We show that Gaia proper motion measurements will easily discriminate between a disk and Galactic center origin, thus allowing us to use HVS17 as a test particle to probe the shape of the Milky Way’s dark matter halo.

Constraints on dark matter annihilations from diffuse gamma-ray emission in the Galaxy

Recent advances in gamma-ray cosmic ray, infrared and radio astronomy have allowed us to develop a significantly better understanding of the galactic medium properties in the last few years. In this work using the DRAGON code, that numerically solves the CR propagation equation and calculating gamma-ray emissivities in a 2-dimensional grid enclosing the Galaxy, we study in a self consistent manner models for the galactic diffuse gamma-ray emission. Our models are cross-checked to both the available CR and gamma-ray data. We address the extend to which dark matter annihilations in the Galaxy can contribute to the diffuse gamma-ray flux towards different directions on the sky. Moreover we discuss the impact that astrophysical uncertainties of non DM nature, have on the derived gamma-ray limits. Such uncertainties are related to the diffusion properties on the Galaxy, the interstellar gas and the interstellar radiation field energy densities. Light ~10 GeV dark matter annihilating dominantly to hadrons is more strongly constrained by gamma-ray observations towards the inner parts of the Galaxy and influenced the most by assumptions of the gas distribution; while TeV scale DM annihilating dominantly to leptons has its tightest constraints from observations towards the galactic center avoiding the galactic disk plane, with the main astrophysical uncertainty being the radiation field energy density. In addition, we present a method of deriving constraints on the dark matter distribution profile from the diffuse gamma-ray spectra. These results critically depend on the assumed mass of the dark matter particles and the type of its end annihilation products.

Fundamental stellar properties from asteroseismology

Accurate characterization of stellar populations is of prime importance to correctly understand the formation and evolution process of our Galaxy. The field of asteroseismology has been particularly successful in such an endeavor providing fundamental parameters for large samples of stars in different evolutionary phases. We present our results on determinations of masses, radii, and distances of stars in the CoRoT and Kepler fields, showing that we can map and date different regions of the galactic disk and distinguish gradients in the distribution of stellar properties at different heights. We further review how asteroseismic determinations can produce a unique set of constraints, including ages, outside the solar neighborhood for galactic chemical evolution models.

The white dwarf cooling sequence of the Galactic bulge

We collected F606W- and F814W-band time-series data of the Sagittarius low-reddening window in the Galactic bulge with the Advanced Camera far Surveys mounted on the Hubble Space Telescope. We sampled the region approximately every two weeks for one year, with the principal aim to detect a hidden population of isolated black holes and neutron stars in the Galactic disk through astrometric microlensing. We present preliminary results here based on a photometric catalog including ~3*10^5 stars down to F606W ~ 31 mag. Proper motions were also measured, with an accuracy of better than ~ 0.5 mas/yr at F606W ~ 28 mag in both coordinates. We were then able to separate disk and bulge stars and to obtain a clean bulge color-magnitude diagram. Together with a dozen candidate extreme horizontal branch stars we were able to identify for the first time a clearly defined white dwarf (WD) cooling sequence in the bulge. The comparison between theory and observations shows that a substantial fraction of the WDs (~40%) is systematically redder than the canonical cooling tracks for CO-core DA WDs. This evidence would suggest the presence of a significant number of He-core WDs in the bulge, formed in close binaries, as has been found in some Galactic globular and open clusters. The presence of close binaries in the bulge population is further supported by the finding of a candidate dwarf nova in outburst and a few candidate cataclysmic variables in quiescence in the same field.

Time variation of the O/H radial gradient in the galactic disk based on planetary nebulae

The controversy on the time variation of the radial abundance gradients can in principle be settled by estimating the gradients from planetary nebulae (PN) ejected by central stars (CSPN) with different ages. In this work, we consider four samples of CSPN whose lifetimes have been estimated using three different methods and estimate the oxygen abundance gradients for these objects. The results suggest some small differences between the younger and older CSPN. The younger objects have similar or slightly higher oxygen abundances compared with the older objects, and the gradients of both groups are similar within the uncertainties. Therefore, the O/H radial gradient has not changed appreciably during the lifetime of the objects considered, so that PN gradients are not expected to be very different from the gradients observed in younger objects, which seems to be supported by recent observational data.

A Galactic Ring of Minimum Stellar Density Near the Solar Orbit Radius

We analyse the secular effects of a long-lived Galactic spiral structure on the stellar orbits with mean radii close to the corotation resonance. By test-particle simulations and different spiral potential models with parameters constrained on observations, we verified the formation of a minimum with amplitude ~ 30% – 40% of the background disk stellar density at corotation. Such minimum is formed by the secular angular momentum transfer between stars and the spiral density wave on both sides of corotation. We demonstrate that the secular loss (gain) of angular momentum and decrease (increase) of mean orbital radius of stars just inside (outside) corotation can counterbalance the opposite trend of exchange of angular momentum shown by stars orbiting the librational points L_4/5 at the corotation circle. Such secular processes actually allow steady spiral waves to promote radial migration across corotation. We propose some observational evidences for the minimum stellar density in the Galactic disk, such as its direct relation to the minimum in the observed rotation curve of the Galaxy at the radius R ~ 9 kpc (for R_0 = 7.5 kpc), as well as its association with a minimum in the distribution of Galactic radii of a sample of open clusters older than 1 Gyr. The closeness of the solar orbit radius to the corotation resonance implies that the solar orbit lies inside a ring of minimum surface density (stellar + gas). This also implies in a correction to larger values for the estimated total mass of the Galactic disk, and consequently, a greater contribution of the disk component to the inner rotation curve of the Galaxy.

Mapping the Three-Dimensional Density of the Galactic Bulge with VVV Red Clump Stars

The inner Milky Way is dominated by a boxy, triaxial bulge which is believed to have formed through disk instability processes. Despite its proximity, its large-scale properties are still not very well known, due to our position in the obscuring Galactic disk. Here we make a measurement of the three-dimensional density distribution of the Galactic bulge using red clump giants identified in DR1 of the VVV survey. Our density map covers the inner (2.2×1.4×1.1)kpc of the bulge/bar. Line-of-sight density distributions are estimated by deconvolving extinction and completeness corrected K-band magnitude distributions. In constructing our measurement, we assume that the three-dimensional bulge is 8-fold mirror triaxially symmetric. In doing so we measure the angle of the bar-bulge to the line-of-sight to be (27+- 2)deg, where the dominant error is systematic arising from the details of the deconvolution process. The resulting density distribution shows a highly elongated bar with projected axis ratios ~(1:2.1) for isophotes reaching ~2kpc along the major axis. Along the bar axes the density falls off roughly exponentially, with axis ratios (10:6.3:2.6) and exponential scale-lengths (0.70:0.44:0.18)kpc. From about 400pc above the Galactic plane, the bulge density distribution displays a prominent X-structure. Overall, the density distribution of the Galactic bulge is characteristic for a strongly boxy/peanut shaped bulge within a barred galaxy.

Giant Molecular Cloud Formation in Disk Galaxies: Characterizing Simulated versus Observed Cloud Catalogues

We present the results of a study of simulated Giant Molecular Clouds (GMCs) formed in a Milky Way-type galactic disk with a flat rotation curve. This simulation, which does not include star formation or feedback, produces clouds with masses ranging between 10^4 Msun and 10^7 Msun. We compare our simulated cloud population to two observational surveys; The Boston University- Five College Radio Astronomy Observatory Galactic Ring Survey and the BIMA All-Disk Survey of M33. An analysis of the global cloud properties as well as a comparison of Larson’s scaling relations is carried out. We find that simulated cloud properties agree well with the observed cloud properties, with the closest agreement occurring between the clouds at comparable resolution in M33. Our clouds are highly filamentary – a property that derives both from their formation due to gravitational instability in the sheared galactic environment, as well as to cloud- cloud gravitational encounters. We also find that the rate at which potentially star forming gas accumulates within dense regions – wherein n_{thresh} > 10^4 cm^{-3} – is 3% per 10 Myr, in clouds of roughly 10^6 Msun. This suggests that star formation rates in observed clouds are related to the rates at which gas can be accumulated into dense subregions within GMCs via filamentary flows. The most internally well-resolved clouds are chosen for listing in a catalogue of simulated GMCs; the first of its kind. The catalogued clouds are available as an extracted data set from the global simulation.

Bimodal chemical evolution of the Galactic disk and the Barium abundance of Cepheids

In order to understand the Barium abundance distribution in the Galactic disk based on Cepheids, one must first be aware of important effects of the corotation resonance, situated a little beyond the solar orbit. The thin disk of the Galaxy is divided in two regions that are separated by a barrier situated at that radius. Since the gas cannot get across that barrier, the chemical evolution is independent on the two sides of it. The barrier is caused by the opposite directions of flows of gas, on the two sides, in addition to a Cassini-like ring void of HI (caused itself by the flows). A step in the metallicity gradient developed at corotation, due to the difference in the average star formation rate on the two sides, and to this lack of communication between them. In connection with this, a proof that the spiral arms of our Galaxy are long-lived (a few billion years) is the existence of this step. When one studies the abundance gradients by means of stars which span a range of ages, like the Cepheids, one has to take into account that stars, contrary to the gas, have the possibility of crossing the corotation barrier. A few stars born on the high metallicity side are seen on the low metallicity one, and vice-versa. In the present work we re-discuss the data on Barium abundance in Cepheids as a function of Galactic radius, taking into account the scenario described above. The [Ba/H] ratio, plotted as a function of Galactic radius, apparently presents a distribution with two branches in the external region (beyond corotation). One can re-interpret the data and attribute the upper branch to the stars that were born on the high metallicity side. The lower branch, analyzed separately, indicates that the stars born beyond corotation have a rising Barium metallicity as a function of Galactic radius.

The High Time Resolution Universe Pulsar Survey - VII: discovery of five millisecond pulsars and the different luminosity properties of binary and isolated recycled pulsars

This paper presents the discovery and timing parameters for five millisecond pulsars (MSPs), four in binary systems with probable white dwarf companions and one isolated, found in ongoing processing of the High Time Resolution Universe Pulsar Survey (HTRU). We also present high quality polarimetric data on four of them. These further discoveries confirm the high potential of our survey in finding pulsars with very short spin periods. At least two of these five MSPs are excellent candidates to be included in the Pulsar Timing Array projects. Thanks to the wealth of MSP discoveries in the HTRU survey, we revisit the question of whether the luminosity distributions of isolated and binary MSPs are different. Using the Cordes and Lazio distance model and our new and catalogue flux density measurements, we find that 41 of the 42 most luminous MSPs in the Galactic disk are in binaries and a statistical analysis suggests that the luminosity functions differ with 99.9% significance. We conclude that the formation process that leads to solitary MSPs affects their luminosities, despite their period and period derivatives being similar to those of pulsars in binary systems.

Planck intermediate results. XIV. Dust emission at millimetre wavelengths in the Galactic plane

We use Planck HFI data combined with ancillary radio data to study the emissivity index of the interstellar dust emission in the frequency range 10 – 353 GHz, or 3 – 0.8 mm, in the Galactic plane. We analyse the region l=20 degr – 44 degr and |b| \leq 4 degr where the free-free emission can be estimated from radio recombination line data. We fit the spectra at each sky pixel with a modified blackbody model and two spectral indices, beta_mm and beta_FIR, below and above 353 GHz respectively. We find that beta_mm is smaller than beta_FIR and we detect a correlation between this low frequency power-law index and the dust optical depth at 353 GHz, tau_353. beta_mm increases from about 1.53 in the more diffuse regions of the Galactic disk, |b| = 3 degr – 4 degr and tau_353 ~ 5 x 10^{-5}, to about 1.65 in the densest regions with an optical depth of more than one order of magnitude higher. We associate this correlation with an evolution of the dust emissivity related to the fraction of molecular gas along the line of sight. This translates into beta_mm ~ 1.53 for a medium which is mostly atomic and beta_mm ~ 1.65 when the medium is dominated by molecular gas. We find that both the Two-Level System model and the emission by ferromagnetic particles can explain the results if spatial variations of the component or physical processes responsible for the flattening of the dust emission are allowed. The results improve our understanding of the physics of interstellar dust, and lead towards a complete model of the dust spectrum from far-infrared to millimetre wavelengths.

Planck intermediate results. XIV. Dust emission at millimetre wavelengths in the Galactic plane [Replacement]

We use Planck HFI data combined with ancillary radio data to study the emissivity index of the interstellar dust emission in the frequency range 10 – 353 GHz, or 3 – 0.8 mm, in the Galactic plane. We analyse the region l=20 degr – 44 degr and |b| \leq 4 degr where the free-free emission can be estimated from radio recombination line data. We fit the spectra at each sky pixel with a modified blackbody model and two spectral indices, beta_mm and beta_FIR, below and above 353 GHz respectively. We find that beta_mm is smaller than beta_FIR and we detect a correlation between this low frequency power-law index and the dust optical depth at 353 GHz, tau_353. beta_mm increases from about 1.53 in the more diffuse regions of the Galactic disk, |b| = 3 degr – 4 degr and tau_353 ~ 5 x 10^{-5}, to about 1.65 in the densest regions with an optical depth of more than one order of magnitude higher. We associate this correlation with an evolution of the dust emissivity related to the fraction of molecular gas along the line of sight. This translates into beta_mm ~ 1.53 for a medium which is mostly atomic and beta_mm ~ 1.65 when the medium is dominated by molecular gas. We find that both the Two-Level System model and the emission by ferromagnetic particles can explain the results if spatial variations of the component or physical processes responsible for the flattening of the dust emission are allowed. The results improve our understanding of the physics of interstellar dust, and lead towards a complete model of the dust spectrum from far-infrared to millimetre wavelengths.

Dwarf Novae in the OGLE Data. II. Forty New Dwarf Novae in the OGLE-III Galactic Disk Fields

We report the discovery of forty erupting cataclysmic variable stars in the OGLE-III Galactic disk fields. Among them seventeen objects are of U Gem type, four of Z Cam type. Nineteen of the stars show outbursts and superoutbursts typical for SU UMa-type dwarf novae. In the case of five stars we were able to estimate their supercycle lengths. The obtained lengths are in the range 20-90 d, generally between the typical SU UMa-type variables and a few objects classified as the ER UMa-type variables. Since there is no significant difference between the two types but a higher mass-transfer rate resulting in more frequent outbursts and superoutbursts in the ER UMa-type stars, we propose to discard this type as a separate class of variables. We note that in one of the SU UMa-type stars, OGLE-GD-DN-039, we found a negative supercycle period change, in contrast to other active systems of this type. Two of the new OGLE objects showed long-duration WZ Sge-like superoutbursts followed by a sequence of echo outbursts. All stars reported in this paper are part of the OGLE-III Catalog of Variable Stars.

Dwarf Novae in the OGLE Data. II. Forty New Dwarf Novae in the OGLE-III Galactic Disk Fields [Replacement]

We report the discovery of forty erupting cataclysmic variable stars in the OGLE-III Galactic disk fields: seventeen objects of U Gem type, four of Z Cam type, and nineteen stars showing outbursts and superoutbursts typical for SU UMa type dwarf novae. In the case of five stars we were able to estimate their supercycle lengths. The obtained lengths are in the range 20-90 d, generally between the typical SU UMa type variables and a few objects classified as the ER UMa type variables. Since there is no significant difference between the two types but a higher mass-transfer rate resulting in more frequent outbursts and superoutbursts in the ER UMa type stars, we propose to discard this type as a separate class of variables. We note that in one of the SU UMa type stars, OGLE-GD-DN-039, we found a negative supercycle period change, in contrast to other active systems of this type. Two of the new OGLE objects showed long-duration WZ Sge-like superoutbursts followed by a sequence of echo outbursts. All stars reported in this paper are part of the OGLE-III Catalog of Variable Stars.

Galactic Constraints on Supernova Progenitor Models

We undertake a statistical analysis of the radial abundance distributions in the Galactic disk within a theoretical framework for Galactic chemical evolution which incorporates the influence of spiral arms. 1) The mean mass of oxygen ejected per core-collapse SNe (CC SNe) event (which are concentrated within spiral arms) is $\sim$0.27 M$_{\odot}$; 2) the mean mass of iron ejected by `tardy’ Type Ia SNe (SNeIa; progenitors of whom are older/longer-lived stars with ages $\simgt$100 Myr and up to several Gyr, which do not concentrate within spiral arms) is $\sim$0.58 M$_{\odot}$; 3) the upper mass of iron ejected by prompt SNeIa (SNe whose progenitors are younger/shorter-lived stars with ages $\simlt$100 Myr, which are concentrated within spiral arms) is $\leq$0.23 M$_{\odot}$ per event; 4) the corresponding mean mass of iron produced by CC SNe is $\leq$0.04 M$_{\odot}$ per event; (v) short-lived SNe (core-collapse or prompt SNeIa) supply $\sim$85% of the Galactic disk’s iron. The inferred low mean mass of oxygen ejected per CC SNe event implies a low upper mass limit for the corresponding progenitors of $\sim$23 M$_{\odot}$, otherwise the Galactic disk would be overabundant in oxygen. The low mean mass of iron ejected by prompt SNeIa, relative to the mass produced by tardy SNeIa ($\sim$2.5 times lower), prejudices the idea that both sub-populations of SNeIa have the same physical nature. We suggest that, perhaps, prompt SNeIa are more akin to CC SNe, and discuss the implications of such a suggestion.

The Milky Way thin disk structure as revealed by stars and young open clusters

In this contribution I shall focus on the structure of the Galactic thin disk. The evolution of the thin disk and its chemical properties have been discussed in detail by T. Bensby’s contribution in conjunction with the properties of the Galactic thick disk, and by L.Olivia in conjunction with the properties of the Galactic bulge. I will review and discuss the status of our understanding of three major topics, which have been the subject of intense research nowadays, after long years of silence: (1) the spiral structure of the Milky Way, (2) the size of the Galactic disk, and (3) the nature of the Local arm (Orion spur), where the Sun is immersed. The provisional conclusions of this discussion are that : (1) we still have quite a poor knowledge of the Milky Way spiral structure, and the main dis-agreements among various tracers are still to be settled; (2) the Galactic disk does clearly \textit{not} have an obvious luminous cut-off at about 14 kpc from the Galactic center, and next generation Galactic models need to be updated in this respect, and (3) the Local arm is most probably an inter-arm structure, similar to what we see in several external spirals, like M~74. Finally, the impact of GAIA and LAMOST in this field will be briefly discussed as well.

Eclipsing Binary Stars in the OGLE-III Galactic Disk Fields [Replacement]

We present the analysis of 11 589 eclipsing binary stars identified in twenty-one OGLE-III Galactic disk fields toward constellations of Carina, Centaurus, and Musca. All eclipsing binaries but 402 objects are new discoveries. The binaries have out-of-eclipse brightness between I=12.5 mag and I=21 mag. The completeness of the catalog is estimated at a level of about 75%. Comparison of the orbital period distribution for the OGLE-III disk binaries with systems detected in other recent large-scale Galactic surveys shows the maximum around 0.40 d and an almost flat distribution between 0.5 d and 2.5 d, indepedent of population. Ten doubly eclipsing systems and one eclipsing-ellipsoidal object were found among thousands of variables. Nine of them are candidates for quadruple systems. We also identify ten eclipsing subdwarf-B type binary stars and numerous eclipsing RS CVn type variables. All objects reported in this paper are part of the OGLE-III Catalog of Variable Stars.

Eclipsing Binary Stars in the OGLE-III Galactic Disk Fields

We present the analysis of 11,589 eclipsing binary stars identified in 21 OGLE-III Galactic disk fields toward constellations of Carina, Centaurus, and Musca. All eclipsing binaries but 393 objects are new discoveries. The binaries have out-of-eclipse brightness between I=12.5 and I=21 mag. The completeness of the catalog is estimated at a level of about 75%. Comparison of the orbital period distribution for the OGLE-III disk binaries with systems detected in other recent large-scale Galactic surveys shows the maximum around 0.40 d and an almost flat distribution between 0.5 and 2.5 d, indepedent of population. Among thousands of variables we have found 10 doubly eclipsing objects and one eclipsing-ellipsoidal object, of which 9 are candidates for quadruple systems. We also identify 10 eclipsing subdwarf-B-type binary stars and numerous eclipsing RS Canum-Venaticorum-type variables. All objects reported in this paper are part of the OGLE-III Catalog of Variable Stars.

Explaining two circumnuclear star forming rings in NGC5248

The distribution of gas in the central kiloparsec of a galaxy has a dynamically rapid evolution. Nonaxisymmetries in the gravitational potential of the galactic disk, such as a large scale stellar bar or spiral, can lead to significant radial motion of gaseous material from larger radii to the central region. The large influx of gas and the subsequent star formation keep the central region constantly changing. However, the ability of gas to reach the nucleus proper to fuel an AGN phase is not guaranteed. Gas inflow can be halted at a circumnuclear star forming ring several hundred parsec away. The nearby galaxy NGC5248 is especially interesting in this sense since it is said to host 2 circumnuclear star forming rings at 100pc and 370pc from its quiescent nucleus. Here we present new subarcsecond PdBI+30m CO(2-1) emission line observations of the central region. For the first time the molecular gas distribution at the smallest stellar ring is resolved into a gas ring, consistent with the presence of a quiescent nucleus. However, the molecular gas shows no ring structure at the larger ring. We combine analyses of the gaseous and stellar content in the central kiloparsec of this galaxy to understand the gas distribution and dynamics of this star forming central region. We discuss the probability of two scenarios leading to the current observations, given our full understanding of this system, and discuss whether there are really two circumnuclear star forming rings in this galaxy.

Luminosities of radio Pulsars

Luminosity is an intrinsic property of radio pulsars related to the properties of the magnetospheric plasma and the beam geometry, and inversely proportional to the observing frequency. In traditional models, luminosity has been considered as a function of the spin parameters of pulsars. On the other hand, parameter independent models like power law and lognormal have been also used to fit the observed luminosities. Some of the older studies on pulsar luminosities neglected observational biases, but all of the recent studies tried to model observational effects as accurately as possible. Luminosities of pulsars in globular clusters and in the Galactic disk have been studied separately. Older studies concluded that these two categories of pulsars have different luminosity distributions, but the most recent study concluded that those are the same. This article reviews all significant works on pulsar luminosities and discusses open questions.

A Spectroscopic Analysis of the Eclipsing Short-Period Binary v505 Per and the Origin of the Lithium Dip

As a test of rotationally-induced mixing causing the well-known Li dip in older mid-F dwarfs in the local Galactic disk, we utilize high-resolution and -S/N Keck/HIRESspectroscopy to measure the Li abundance in the components of the1 Gyr, [Fe/H]=-0.15 eclipsing short-period binary V505 Per. We find A(Li)=2.7+/-0.1 and 2.4+/-0.2 in the Teff=6500 and 6450 K primary and secondary components, respectively. Previous Teff determinations and uncertainties suggest that each component is located in the midst of the Li dip. If so, their A(Li) are >=2-5 times larger than A(Li) detections and upper limits observed in the similar metallicity and intermediate-age open clusters NGC 752 and 3680, as well as the more metal-rich and younger Hyades and Praesepe. These differences are even larger if the consistent estimates of the scaling ofinitial Li with metallicity inferred from nearby disk stars, open clusters, and recent Galactic chemical evolution models are correct. Our results suggest, independently of complementary evidence based on Li/Be ratios, Be/B ratios, and Li in subgiants evolving out of the Li dip, that main-sequence angular momentum evolution is the origin of the Li dip. Specifically, our stars’ A(Li) indicates tidal synchronization can be sufficiently efficient and occur early enough in short-period binary mid-F stars to reduce the effects of rotationally-induced mixing and destruction of Li occuring during the main-sequence in otherwise similar stars that are not short-period tidally-locked binaries.

Sejong Open Cluster Survey (SOS). 0. Target Selection and Data Analysis

Star clusters are superb astrophysical laboratories containing cospatial and coeval samples of stars with similar chemical composition. We have initiated the Sejong Open cluster Survey (SOS) – a project dedicated to providing homogeneous photometry of a large number of open clusters in the SAAO Johnson-Cousins’ $UBVI$ system. To achieve our main goal, we have paid much attention to the observation of standard stars in order to reproduce the SAAO standard system. Many of our targets are relatively small, sparse clusters that escaped previous observations. As clusters are considered building blocks of the Galactic disk, their physical properties such as the initial mass function, the pattern of mass segregation, etc. give valuable information on the formation and evolution of the Galactic disk. The spatial distribution of young open clusters will be used to revise the local spiral arm structure of the Galaxy. In addition, the homogeneous data can also be used to test stellar evolutionary theory, especially concerning rare massive stars. In this paper we present the target selection criteria, the observational strategy for accurate photometry, and the adopted calibrations for data analysis such as color-color relations, zero-age main sequence relations, Sp – Mv relations, Sp – Teff relations, Sp – color relations, and Teff – BC relations. Finally we provide some data analysis such as the determination of the reddening law, the membership selection criteria, and distance determination.

 

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