Posts Tagged stellar parameters

Recent Postings from stellar parameters

Stellar granulation and interferometry

Stars are not smooth. Their photosphere is covered by a granulation pattern associated with the heat transport by convection. The convection-related surface structures have different size, depth, and temporal variations with respect to the stellar type. The related activity (in addition to other phenomena such as magnetic spots, rotation, dust, etc.) potentially causes bias in stellar parameters determination, radial velocity, chemical abundances determinations, and exoplanet transit detections. The role of long-baseline interferometric observations in this astrophysical context is crucial to characterize the stellar surface dynamics and correct the potential biases. In this Chapter, we present how the granulation pattern is expected for different kind of stellar types ranging from main sequence to extremely evolved stars of different masses and how interferometric techniques help to study their photospheric dynamics.

A spectroscopic survey of Herbig Ae/Be stars with X-Shooter I: Stellar parameters and accretion rates

Herbig Ae/Be stars span a key mass range that links low and high mass stars, and thus provide an ideal window from which to explore their formation. This paper presents VLT/X-Shooter spectra of 91 Herbig Ae/Be stars, HAeBes; the largest spectroscopic study of HAeBe accretion to date. A homogeneous approach to determining stellar parameters is undertaken for the majority of the sample. Measurements of the ultra-violet (UV) are modelled within the context of magnetospheric accretion, allowing a direct determination of mass accretion rates. Multiple correlations are observed across the sample between accretion and stellar properties: the youngest and often most massive stars are the strongest accretors, and there is an almost 1:1 relationship between the accretion luminosity and stellar luminosity. Despite these overall trends of increased accretion rates in HAeBes when compared to classical T Tauri stars, we also find noticeable differences in correlations when considering the Herbig Ae and Herbig Be subsets. This, combined with the difficulty in applying a magnetospheric accretion model to some of the Herbig Be stars, could suggest that another form of accretion may be occurring within the Herbig Be mass range.

Bayesian Statistics as a New Tool for Spectral Analysis: I. Application for the Determination of Basic Parameters of Massive Stars

Spectral analysis is a powerful tool to investigate stellar properties and it has been widely used for decades now. However, the methods considered to perform this kind of analysis are mostly based on iteration among a few diagnostic lines to determine the stellar parameters. While these methods are often simple and fast, they can lead to errors and large uncertainties due to the required assumptions. Here we present a method based on Bayesian statistics to find simultaneously the best combination of effective temperature, surface gravity, projected rotational velocity, and microturbulence velocity, using all the available spectral lines. Different tests are discussed to demonstrate the strength of our method, which we apply to 54 mid-resolution spectra of field and cluster B stars obtained at the Observatoire du Mont-M\’egantic. We compare our results with those found in the literature. Differences are seen which are well explained by the different methods used. We conclude that the B-star microturbulence velocities are often underestimated. We also confirm the trend that B stars in clusters are on average faster rotators than field B stars.

Grid Search in Stellar Parameters: a software for spectrum analysis of single stars and binary systems

The currently operating space missions, as well as those that will be launched in the near future, (will) deliver high-quality data for millions of stellar objects. Since the majority of stellar astrophysical applications still (at least partly) rely on spectroscopic data, an efficient tool for the analysis of medium- to high-resolution spectroscopy is needed. We aim at developing an efficient software package for the analysis of medium- to high-resolution spectroscopy of single stars and those in binary systems. The major requirements are that the code has a high performance, represents the state-of-the-art analysis tool, and provides accurate determinations of atmospheric parameters and chemical compositions for different types of stars. We use the method of atmosphere models and spectrum synthesis, which is one of the most commonly used approaches for the analysis of stellar spectra. Our Grid Search in Stellar Parameters (GSSP) code makes use of the OpenMPI implementation, which makes it possible to run in parallel mode. The method is first tested on the simulated data and is then applied to the spectra of real stellar objects. The majority of test runs on the simulated data were successful in the sense that we could recover the initially assumed sets of atmospheric parameters. We experimentally find the limits in signal-to-noise ratios of the input spectra, below which the final set of parameters gets significantly affected by the noise. Application of the GSSP package to the spectra of three Kepler stars, KIC11285625, KIC6352430, and KIC4931738, was also largely successful. We found an overall agreement of the final sets of the fundamental parameters with the original studies. For KIC6352430, we found that dependence of the light dilution factor on wavelength cannot be ignored, as it has significant impact on the determination of the atmospheric parameters of this binary system.

Abundances in the Local Region I: G and K Giants

Parameters and abundances for 1133 stars of spectral types F, G, and K of luminosity class III have been derived. In terms of stellar parameters, the primary point of interest is the disagreement between gravities derived with masses determined from isochrones, and gravities determined from an ionization balance. This is not a new result per se; but the size of this sample emphasizes the severity of the problem. A variety of arguments lead to the selection of the ionization balance gravity as the working value. The derived abundances indicate that the giants in the solar region have Sun-like total abundances and abundance ratios. Stellar evolution indicators have also been investigated with the Li abundances and the [C/Fe] and C/O ratios indicating that standard processing has been operating in these stars. The more salient result for stellar evolution is that the [C/Fe] data across the red-giant clump indicates the presence of mass dependent mixing in accord with standard stellar evolution predictions. Keywords: stars: fundamental parameters – stars: abundances – stars: evolution – Galaxy: abundances

The nature of the KFR08 stellar stream

The origin of a new kinematically identified metal-poor stellar stream, the KFR08 stream, has not been established. We present stellar parameters, stellar ages, and detailed elemental abundances for Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Ni, Zn, Sr, Y, Zr, Ba, La, and Eu for 16 KFR08 stream members based on analysis of high resolution spectra. Based on the abundance ratios of 14 elements, we use the chemical tagging method to identify the stars which have the same chemical composition, and thus, might have a common birthplace, such as a cluster. Although three stars were tagged with similar elemental abundances ratios, we find that, statistically, it is not certain that they originate from a dissolved star cluster. This conclusion is consistent with the large dispersion of [Fe/H] ($\sigma_{\rm{[Fe/H]}} = 0.29$) among the 16 stream members. We find that our stars are $\alpha$ enhanced and that the abundance patterns of the stream members are well matched to the thick disk. In addition, most of the stream stars have estimated stellar ages larger than 11 Gyr. These results, together with the hot kinematics of the stream stars, suggest that the KFR08 stream is originated from the thick disk population which was perturbed by a massive merger in the early universe.

Discovery of a strongly r-process enhanced extremely metal-poor star LAMOST J110901.22+075441.8

We report the discovery of an extremely metal-poor (EMP) giant, LAMOST J110901.22+075441.8, which exhibits large excess of r-process elements with [Eu/Fe] ~ +1.16. The star is one of the newly discovered EMP stars identified from LAMOST low-resolution spectroscopic survey and the high-resolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22+075441.8. The abundance pattern of LAMOST J110901.22+075441.8 in the range of C through Zn is in line with the "normal" population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22+075441.8 is in agreement with other well studied cool r-II metal-poor giants such as CS 22892-052 and CS 31082-001. The abundances of elements in the range from Ba through Dy well match the scaled Solar r-process pattern. LAMOST J110901.22+075441.8 provides the first detailed measurements of neutron-capture elements among r-II stars at such low metallicity with [Fe/H]<-3.4, and exhibits similar behavior in the abundance ratio of Zr/Eu as well as Sr/Eu and Ba/Eu as other r-II stars.

On the rotation periods of the components of the triple system TYC9300-0891-1AB/TYC9300-0529-1 in the Octans Association

Stellar rotation depends on different parameters. The range of values of these parameters causes the dispersion in the rotation period distributions observed in young stellar clusters/associations. We focus our investigation on the effects of different circumstellar environments on stellar rotation. More specifically, we are searching in stellar Associations for visual triple systems where all stellar parameters are similar, with the only exceptions of the unknown initial rotation period, and of the circum-stellar environment, in the sense that one of the two about equal-mass components has a close-by third ‘perturber’ component. In the present study we analyse the 35-Myr old visual triple system TYC 9300-0891-1AB + TYC 9300-0529-1 in the young Octans stellar association consisting of three equal-mass K0V components. We collected from the literature all information that allowed us to infer that the three components are actually physically bound forming a triple system and are members of the Octans Association. We collected broad-band photometric timeseries in two observation seasons. We discovered that all the components are variable, magnetically active, and from periodogram analysis we found the unresolved components TYC 9300-0891-1AB to have a rotation period P = 1.383d and TYC 9300-0529-1 a rotation period P = 1.634d. TYC 9300-0891-1A, TYC 9300-0891-1B, and TYC 9300-0529-1 have same masses, ages, and initial chemical compositions. The relatively small 16% rotation period difference measured by us indicates that all components had similar initial rotation periods and disc lifetimes, and the separation of 157AU between the component A and the ‘perturber’ component B (or vice-versa) has been sufficiently large to prevent any significant perturbation/shortening of the accretion-disc lifetime.

Stellar parameters for stars of the CoRoT exoplanet field

Aims:To support the computation and evolutionary interpretation of periods associated with the rotational modulation, oscillations, and variability of stars located in the CoRoT fields, we are conducting a spectroscopic survey for stars located in the fields already observed by the satellite. These observations allow us to compute physical and chemical parameters for our stellar sample. Method: Using spectroscopic observations obtained with UVES/VLT and Hydra/Blanco, and based on standard analysis techniques, we computed physical and chemical parameters ($T_{\rm{eff}}$, $\log \,(g)$, $\rm{[Fe/H]}$, $v_{\rm{mic}}$, $v_{\rm{rad}}$, $v \sin \,(i)$, and $A(\rm{Li})$) for a large sample of CoRoT targets. Results: We provide physical and chemical parameters for a sample comprised of 138 CoRoT targets. Our analysis shows the stars in our sample are located in different evolutionary stages, ranging from the main sequence to the red giant branch, and range in spectral type from F to K. The physical and chemical properties for the stellar sample are in agreement with typical values reported for FGK stars. However, we report three stars presenting abnormal lithium behavior in the CoRoT fields. These parameters allow us to properly characterize the intrinsic properties of the stars in these fields. Our results reveal important differences in the distributions of metallicity, $T_{\rm eff}$, and evolutionary status for stars belonging to different CoRoT fields, in agreement with results obtained independently from ground-based photometric surveys. Conclusions: Our spectroscopic catalog, by providing much-needed spectroscopic information for a large sample of CoRoT targets, will be of key importance for the successful accomplishment of several different programs related to the CoRoT mission, thus it will help further boost the scientific return associated with this space mission.

Asteroseismic analysis of solar-mass subgiants KIC 6442183 and KIC 11137075 observed by Kepler

Asteroseismology provides a powerful way to constrain stellar parameters. Solar-like oscillations have been observed on subgiant stars with the \emph{Kepler\/} mission. The continuous and high-precision time series enables us to carry out a detailed asteroseismic study for these stars. We carry out data processing of two subgiants of spectral type G: KIC 6442183 and KIC 11137075 observed with the \emph{Kepler} mission, and perform seismic analysis for the two evolved stars. We estimate the values of global asteroseismic parameters: $\Delta\nu=64.9\pm 0.2 $ $\mu$Hz and $\nu_{\rm max}=1225 \pm 17$ $\mu$Hz for KIC 6442183, $\Delta\nu=65.5\pm 0.2 $ $\mu$Hz and $\nu_{\rm max}=1171 \pm 8$ $\mu$Hz for KIC 11137075, respectively. In addition, we extract the individual mode frequencies of the two stars. We compare stellar models and observations, including mode frequencies and mode inertias. The mode inertias of mixed modes, which are sensitive to the stellar interior, are used to constrain stellar models. We define a quantity $d\nu_{\rm m-p}$ that measures the difference between the mixed modes and the expected pure pressure modes, which is related to the inertia ratio of mixed modes to radial modes. Asteroseismic together with spectroscopic constraints provide the estimations of the stellar parameters: $M = 1.04_{-0.04}^{+0.01} M_{\odot}$, $R = 1.66_{-0.02}^{+0.01} R_{\odot}$ and $t=8.65_{-0.06}^{+1.12}$ Gyr for KIC 6442183, and $M = 1.00_{-0.01}^{+0.01} M_{\odot}$, $R = 1.63_{-0.01}^{+0.01} R_{\odot}$ and $t=10.36_{-0.20}^{+0.01}$ Gyr for KIC 11137075. Either mode inertias or $d\nu_{\rm m-p}$ could be used to constrain stellar models.

Asteroseismic analysis of solar-mass subgiants KIC 6442183 and KIC 11137075 observed by Kepler [Replacement]

Asteroseismology provides a powerful way to constrain stellar parameters. Solar-like oscillations have been observed on subgiant stars with the \emph{Kepler\/} mission. The continuous and high-precision time series enables us to carry out a detailed asteroseismic study for these stars. We carry out data processing of two subgiants of spectral type G: KIC 6442183 and KIC 11137075 observed with the \emph{Kepler} mission, and perform seismic analysis for the two evolved stars. We estimate the values of global asteroseismic parameters: $\Delta\nu=64.9\pm 0.2 $ $\mu$Hz and $\nu_{\rm max}=1225 \pm 17$ $\mu$Hz for KIC 6442183, $\Delta\nu=65.5\pm 0.2 $ $\mu$Hz and $\nu_{\rm max}=1171 \pm 8$ $\mu$Hz for KIC 11137075, respectively. In addition, we extract the individual mode frequencies of the two stars. We compare stellar models and observations, including mode frequencies and mode inertias. The mode inertias of mixed modes, which are sensitive to the stellar interior, are used to constrain stellar models. We define a quantity $d\nu_{\rm m-p}$ that measures the difference between the mixed modes and the expected pure pressure modes, which is related to the inertia ratio of mixed modes to radial modes. Asteroseismic together with spectroscopic constraints provide the estimations of the stellar parameters: $M = 1.04_{-0.04}^{+0.01} M_{\odot}$, $R = 1.66_{-0.02}^{+0.01} R_{\odot}$ and $t=8.65_{-0.06}^{+1.12}$ Gyr for KIC 6442183, and $M = 1.00_{-0.01}^{+0.01} M_{\odot}$, $R = 1.63_{-0.01}^{+0.01} R_{\odot}$ and $t=10.36_{-0.20}^{+0.01}$ Gyr for KIC 11137075. Either mode inertias or $d\nu_{\rm m-p}$ could be used to constrain stellar models.

Estimation of distances to stars with stellar parameters from LAMOST

We present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star’s absolute magnitude. This technique is tailored specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ~5-degree diameter "plate" that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ~20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ~40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.

The Araucaria Project. Accurate stellar parameters and distance to evolved eclipsing binary ASAS J180057-2333.8 in Sagittarius Arm

We have analyzed the double-lined eclipsing binary system ASAS J180057-2333.8 from the All Sky Automated Survey (ASAS) catalogue . We measure absolute physical and orbital parameters for this system based on archival $V$-band and $I$-band ASAS photometry, as well as on high-resolution spectroscopic data obtained with ESO 3.6m/HARPS and CORALIE spectrographs. The physical and orbital parameters of the system were derived with an accuracy of about 0.5 – 3%. The system is a very rare configuration of two bright well-detached giants of spectral types K1 and K4 and luminosity class II. The radii of the stars are $R_1$ = 52.12 $\pm$ 1.38 and $R_2$ = 67.63 $\pm$ 1.40 R$_\odot$ and their masses are $M_1$ = 4.914 $\pm$ 0.021 and $M_2$ = 4.875$\pm$ 0.021 M$_\odot$ . The exquisite accuracy of 0.5% obtained for the masses of the components is one of the best mass determinations for giants. We derived a precise distance to the system of 2.14 $\pm$ 0.06 kpc (stat.) $\pm$ 0.05 (syst.) which places the star in the Sagittarius-Carina arm. The Galactic rotational velocity of the star is $\Theta_s=258 \pm 26$ km s$^{-1}$ assuming $\Theta_0=238$ km s$^{-1}$. A comparison with PARSEC isochrones places the system at the early phase of core helium burning with an age of slightly larger than 100 million years. The effect of overshooting on stellar evolutionary tracks was explored using the MESA star code.

The Araucaria Project. Accurate stellar parameters and distance to evolved eclipsing binary ASAS J180057-2333.8 in Sagittarius Arm [Replacement]

We have analyzed the double-lined eclipsing binary system ASAS J180057-2333.8 from the All Sky Automated Survey (ASAS) catalogue . We measure absolute physical and orbital parameters for this system based on archival $V$-band and $I$-band ASAS photometry, as well as on high-resolution spectroscopic data obtained with ESO 3.6m/HARPS and CORALIE spectrographs. The physical and orbital parameters of the system were derived with an accuracy of about 0.5 – 3%. The system is a very rare configuration of two bright well-detached giants of spectral types K1 and K4 and luminosity class II. The radii of the stars are $R_1$ = 52.12 $\pm$ 1.38 and $R_2$ = 67.63 $\pm$ 1.40 R$_\odot$ and their masses are $M_1$ = 4.914 $\pm$ 0.021 and $M_2$ = 4.875$\pm$ 0.021 M$_\odot$ . The exquisite accuracy of 0.5% obtained for the masses of the components is one of the best mass determinations for giants. We derived a precise distance to the system of 2.14 $\pm$ 0.06 kpc (stat.) $\pm$ 0.05 (syst.) which places the star in the Sagittarius-Carina arm. The Galactic rotational velocity of the star is $\Theta_s=258 \pm 26$ km s$^{-1}$ assuming $\Theta_0=238$ km s$^{-1}$. A comparison with PARSEC isochrones places the system at the early phase of core helium burning with an age of slightly larger than 100 million years. The effect of overshooting on stellar evolutionary tracks was explored using the MESA star code.

Identification of Globular Cluster Stars in RAVE data I: Application to Stellar Parameter Calibration

We present the identification of potential members of nearby Galactic globular clusters using radial velocities from the RAdial Velocity Experiment Data Release 4 (RAVE-DR4) survey database. Our identifications are based on three globular clusters — NGC 3201, NGC 5139 ($\omega$ Cen) and NGC 362 — all of which are shown to have |RV|>100 km/s. The identification of globular cluster stars in RAVE DR4 data offers a unique opportunity to test the precision and accuracy of the stellar parameters determined with the currently available Stellar Parameter Pipelines (SPPs) used in the survey, as globular clusters are ideal testbeds for the validation of stellar atmospheric parameters, abundances, distances and ages. For both NGC 3201 and $\omega$ Cen, there is compelling evidence for numerous members (> 10) in the RAVE database; in the case of NGC 362 the evidence is more ambiguous, and there may be significant foreground and/or background contamination in our kinematically-selected sample. A comparison of the RAVE-derived stellar parameters and abundances with published values for each cluster and with BASTI isochrones for ages and metallicities from the literature reveals overall good agreement, with the exception of the apparent underestimation of surface gravities for giants, in particular for the most metal-poor stars. Moreover, if the selected members are part of the main body of each cluster our results would also suggest that the distances from Binney et al. 2013, where only isochrones more metal-rich than -0.9 dex were used, are typically underestimated by ~ 40% with respect to the published distances for the clusters, while the distances from Zwitter et al. 2010 show stars ranging from 1 to ~ 6.5 kpc — with indications of a trend toward higher distances at lower metallicities — for the three clusters analysed in this study.

New OB star candidates in the Carina Arm around Westerlund 2 from VPHAS+

O and early B stars are at the apex of galactic ecology, but in the Milky Way, only a minority of them may yet have been identified. We present the results of a pilot study to select and parametrise OB star candidates in the Southern Galactic plane, down to a limiting magnitude of $g=20$. A 2 square-degree field capturing the Carina Arm around the young massive star cluster, Westerlund 2, is examined. The confirmed OB stars in this cluster are used to validate our identification method, based on selection from the $(u-g, g-r)$ diagram for the region. Our Markov Chain Monte Carlo fitting method combines VPHAS+ $u, g, r, i$ with published $J, H, K$ photometry in order to derive posterior probability distributions of the stellar parameters $\log(\rm T_{\rm eff})$ and distance modulus, together with the reddening parameters $A_0$ and $R_V$. The stellar parameters are sufficient to confirm OB status while the reddening parameters are determined to a precision of $\sigma(A_0)\sim0.09$ and $\sigma(R_V)\sim0.08$. There are 489 objects that fit well as new OB candidates, earlier than $\sim$B2. This total includes 74 probable massive O stars, 5 likely blue supergiants and 32 reddened subdwarfs. This increases the number of previously known and candidate OB stars in the region by nearly a factor of 10. Most of the new objects are likely to be at distances between 3 and 6 kpc. We have confirmed the results of previous studies that, at these longer distances, these sight lines require non-standard reddening laws with $3.5<R_V<4$.

Transiting exoplanets from the CoRoT space mission XXVIII. CoRoT-28b, a planet orbiting an evolved star, and CoRoT-29b, a planet showing an asymmetric transit

Context. We present the discovery of two transiting extrasolar planets by the satellite CoRoT. Aims. We aim at a characterization of the planetary bulk parameters, which allow us to further investigate the formation and evolution of the planetary systems and the main properties of the host stars. Methods. We used the transit light curve to characterize the planetary parameters relative to the stellar parameters. The analysis of HARPS spectra established the planetary nature of the detections, providing their masses. Further photometric and spectroscopic ground-based observations provided stellar parameters (log g,Teff,v sin i) to characterize the host stars. Our model takes the geometry of the transit to constrain the stellar density into account, which when linked to stellar evolutionary models, determines the bulk parameters of the star. Because of the asymmetric shape of the light curve of one of the planets, we had to include the possibility in our model that the stellar surface was not strictly spherical. Results. We present the planetary parameters of CoRoT-28b, a Jupiter-sized planet (mass 0.484+/-0.087MJup; radius 0.955+/-0.066RJup) orbiting an evolved star with an orbital period of 5.208 51 +/- 0.000 38 days, and CoRoT-29b, another Jupiter-sized planet (mass 0.85 +/- 0.20MJup; radius 0.90 +/- 0.16RJup) orbiting an oblate star with an orbital period of 2.850 570 +/- 0.000 006 days. The reason behind the asymmetry of the transit shape is not understood at this point. Conclusions. These two new planetary systems have very interesting properties and deserve further study, particularly in the case of the star CoRoT-29.

Transiting exoplanets from the CoRoT space mission XXVII. CoRoT-28b, a planet orbiting an evolved star, and CoRoT-29b, a planet showing an asymmetric transit [Replacement]

Context. We present the discovery of two transiting extrasolar planets by the satellite CoRoT. Aims. We aim at a characterization of the planetary bulk parameters, which allow us to further investigate the formation and evolution of the planetary systems and the main properties of the host stars. Methods. We used the transit light curve to characterize the planetary parameters relative to the stellar parameters. The analysis of HARPS spectra established the planetary nature of the detections, providing their masses. Further photometric and spectroscopic ground-based observations provided stellar parameters (log g,Teff,v sin i) to characterize the host stars. Our model takes the geometry of the transit to constrain the stellar density into account, which when linked to stellar evolutionary models, determines the bulk parameters of the star. Because of the asymmetric shape of the light curve of one of the planets, we had to include the possibility in our model that the stellar surface was not strictly spherical. Results. We present the planetary parameters of CoRoT-28b, a Jupiter-sized planet (mass 0.484+/-0.087MJup; radius 0.955+/-0.066RJup) orbiting an evolved star with an orbital period of 5.208 51 +/- 0.000 38 days, and CoRoT-29b, another Jupiter-sized planet (mass 0.85 +/- 0.20MJup; radius 0.90 +/- 0.16RJup) orbiting an oblate star with an orbital period of 2.850 570 +/- 0.000 006 days. The reason behind the asymmetry of the transit shape is not understood at this point. Conclusions. These two new planetary systems have very interesting properties and deserve further study, particularly in the case of the star CoRoT-29.

RAVE as a Gaia precursor: what to expect from the Gaia RVS?

The Radial Velocity Experiment (RAVE) is a large wide-field spectroscopic stellar survey of the Milky Way. Over the period 2003-2013, 574,630 spectra for 483,330 stars have been amassed at a resolution of R=7500 in the Ca-triplet region of 8410-8795\AA. Wavelength coverage and resolution are thus comparable to that anticipated from the Gaia RVS. Derived data products of RAVE include radial velocities, stellar parameters, chemicals abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni, and absorption measures based on the diffuse interstellar bands (DIB) at 8620\AA. Since more than 290000 RAVE targets are drawn from the Tycho-2 catalogue, RAVE will be an interesting prototype for the anticipated full Gaia data releases, in particular when combined with the early Gaia data releases, which contain astrometry but not yet stellar parameters and abundances.

Spectroscopic study of red giants in the Kepler field with asteroseismologically established evolutionary status and stellar parameters

Thanks to the recent very high-precision photometry of red giants from satellites such as Kepler, precise mass and radius values as well as accurate information of evolutionary stages are already established by asteroseismic approach for a large number of G-K giants. Based on the high-dispersion spectra of selected such 55 red giants in the Kepler field with precisely known seismic parameters (among which parallaxes are available for 9 stars), we checked the accuracy of the determination method of stellar parameters previously applied to many red giants by Takeda et al. (2008, PASJ, 60, 781), since it may be possible to discriminate their complex evolutionary status by using the surface gravity vs. mass diagram. We confirmed that our spectroscopic gravity and the seismic gravity satisfactorily agree with each other (to within ~0.1 dex) without any systematic difference. However, the mass values of He-burning red clump giants derived from stellar evolutionary tracks (~2-3 Msun) were found to be markedly larger by ~50% compared to the seismic values (~1-2 Msun) though such discrepancy is not seen for normal giants in the H-burning phase, which reflects the difficulty of mass determination from intricately overlapping tracks on the luminosity vs. effective temperature diagram. This consequence implies that the mass results of many red giants in the clump region determined by Takeda et al. (2008) are likely to be significantly overestimated. We also compare our spectroscopically established parameters with recent literature values, and further discuss the prospect of distinguishing the evolutionary status of red giants based on the conventional (i.e., non-seismic) approach.

Detailed Abundances of 15 Stars in the Metal-Poor Globular Cluster NGC 4833

We have observed 15 red giant stars in the relatively massive, metal-poor globular cluster NGC 4833 using the MIKE spectrograph at Magellan. We calculate stellar parameters for each star and perform a standard abundance analysis to derive abundances of 43 species of 39 elements, including 20 elements heavier than the iron group. We derive <[Fe/H]> = -2.25 +/- 0.02 from Fe I lines and <[Fe/H> = -2.19 +/- 0.013 from Fe II lines. We confirm earlier results that found no internal metallicity spread in NGC 4833, and there are no significant star-to-star abundance dispersions among any elements in the iron group (19 <= Z <= 30). We recover the usual abundance variations among the light elements C, N, O, Na, Mg, Al, and possibly Si. The heavy-element distribution reflects enrichment by r-process nucleosynthesis ([Eu/Fe] = +0.36 +/- 0.03), as found in many other metal-poor globular clusters. We investigate small star-to-star variations found among the neutron-capture elements, and we conclude that these are probably not real variations. Upper limits on the Th abundance, log epsilon (Th/Eu) < -0.47 +/- 0.09, indicate that NGC 4833, like other globular clusters where Th has been studied, did not experience a so-called "actinide boost."

Detailed Abundances of 15 Stars in the Metal-Poor Globular Cluster NGC 4833 [Replacement]

We have observed 15 red giant stars in the relatively massive, metal-poor globular cluster NGC 4833 using the Magellan Inamori Kyocera Echelle spectrograph at Magellan. We calculate stellar parameters for each star and perform a standard abundance analysis to derive abundances of 43 species of 39 elements, including 20 elements heavier than the iron group. We derive <[Fe/H]> = -2.25 +/- 0.02 from Fe I lines and <[Fe/H> = -2.19 +/- 0.013 from Fe II lines. We confirm earlier results that found no internal metallicity spread in NGC 4833, and there are no significant star-to-star abundance dispersions among any elements in the iron group (19 <= Z <= 30). We recover the usual abundance variations among the light elements C, N, O, Na, Mg, Al, and possibly Si. The heavy-element distribution reflects enrichment by r-process nucleosynthesis ([Eu/Fe] = +0.36 +/- 0.03), as found in many other metal-poor globular clusters. We investigate small star-to-star variations found among the neutron-capture elements, and we conclude that these are probably not real variations. Upper limits on the Th abundance, log epsilon (Th/Eu) < -0.47 +/- 0.09, indicate that NGC 4833, like other globular clusters where Th has been studied, did not experience a so-called "actinide boost."

Stellar parameters of early M dwarfs from ratios of spectral features at optical wavelengths

(Abridged) Low-mass stars have been recognised as promising targets in the search for rocky, small planets with the potential of supporting life. Doppler search programmes using high-resolution spectrographs like HARPS or HARPS-N are providing huge quantities of optical spectra of M dwarfs. We aim to calibrate empirical relationships to determine stellar parameters for early M dwarfs (spectral types M0-M4.5) using the same spectra that are used for the radial velocity determinations. Our methodology consists in the use of ratios of pseudo equivalent widths of spectral features as a temperature diagnostic. Stars with effective temperatures obtained from interferometric estimates of their radii are used as calibrators. Empirical calibrations for the spectral type are also provided. Combinations of features and ratios of features are used to derive calibrations for the stellar metallicity. Our methods are then applied to a large sample of M dwarfs that are being observed in the framework of the HARPS search for extrasolar planets.The derived temperatures and metallicities are used together with photometric estimates of mass, radius, and surface gravity to calibrate empirical relationships for these parameters. A total of 112 temperature sensitive ratios have been calibrated over the range 3100-3950 K, providing Teff values with typical uncertainties of the order of 70 K. Eighty-two ratios of pseudo equivalent widths of features were calibrated to derive spectral types. Regarding stellar metallicity, 696 combinations of pseudo equivalent widths of individual features and temperature-sensitive ratios have been calibrated, over the metallicity range from -0.54 to +0.24 dex, with estimated uncertainties in the range of 0.07-0.10 dex. We provide our own empirical calibrations for stellar mass, radius, and surface gravity.

Stellar Activity and Coronal Heating: an overview of recent results

Observations of the coronae of the Sun and of solar-like stars provide complementary information to advance our understanding of stellar magnetic activity, and of the processes leading to the heating of their outer atmospheres. While solar observations allow us to study the corona at high spatial and temporal resolution, the study of stellar coronae allows us to probe stellar activity over a wide range of ages and stellar parameters. Stellar studies therefore provide us with additional tools for understanding coronal heating processes, as well as the long-term evolution of solar X-ray activity. We discuss how recent studies of stellar magnetic fields and coronae contribute to our understanding of the phenomenon of activity and coronal heating in late-type stars.

Gaia-ESO Survey: The analysis of pre-main sequence stellar spectra

This paper describes the analysis of UVES and GIRAFFE spectra acquired by the Gaia-ESO Public Spectroscopic Survey in the fields of young clusters whose population includes pre-main sequence (PMS) stars. Both methods that have been extensively used in the past and new ones developed in the contest of the Gaia-ESO survey enterprise are available and used. The internal precision of these quantities is estimated by inter-comparing the results obtained by such different methods, while the accuracy is estimated by comparison with independent external data, like effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. Specific strategies are implemented to deal with fast rotation, accretion signatures, chromospheric activity, and veiling. The analysis carried out on spectra acquired in young clusters’ fields during the first 18 months of observations, up to June 2013, is presented in preparation of the first release of advanced data products. Stellar parameters obtained with the higher resolution and larger wavelength coverage from UVES are reproduced with comparable accuracy and precision using the smaller wavelength range and lower resolution of the GIRAFFE setup adopted for young stars, which allows us to provide with confidence stellar parameters for the much larger GIRAFFE sample. Precisions are estimated to be $\approx$ 120 K r.m.s. in Teff, $\approx$0.3 dex r.m.s. in logg, and $\approx$0.15 dex r.m.s. in [Fe/H], for both the UVES and GIRAFFE setups.

Abundances, Stellar Parameters, and Spectra From the SDSS-III/APOGEE Survey

The SDSS-III/APOGEE survey operated from 2011-2014 using the APOGEE spectrograph, which collects high-resolution (R~22,500), near-IR (1.51-1.70 microns) spectra with a multiplexing (300 fiber-fed objects) capability. We describe the survey data products that are publicly available, which include catalogs with radial velocity, stellar parameters, and 15 elemental abundances for over 150,000 stars, as well as the more than 500,000 spectra from which these quantities are derived. Calibration relations for the stellar parameters (Teff, log g, [M/H], [alpha/M]) and abundances (C, N, O, Na, Mg, Al, Si, S, K, Ca, Ti, V, Mn, Fe, Ni) are presented and discussed. The internal scatter of the abundances within clusters indicates that abundance precision is generally between 0.05 and 0.09 dex across a broad temperature range; within more limited ranges and at high S/N, it is smaller for some elemental abundances. We assess the accuracy of the abundances using comparison of mean cluster metallicities with literature values, APOGEE observations of the solar spectrum and of Arcturus, comparison of individual star abundances with other measurements, and consideration of the locus of derived parameters and abundances of the entire sample, and find that it is challenging to determine the absolute abundance scale; external accuracy may be good to 0.1-0.2 dex. Uncertainties may be larger at cooler temperatures (Teff<4000K). Access to the public data release and data products is described, and some guidance for using the data products is provided.

Abundance Differences Between Exoplanet Binary Host Stars XO-2N and XO-2S -- Dependence on Stellar Parameters

The chemical composition of exoplanet host stars is an important factor in understanding the formation and characteristics of their orbiting planets. The best example of this to date is the planet-metallicity correlation. Other proposed correlations are thus far less robust, in part due to uncertainty in the chemical history of stars pre- and post-planet formation. Binary host stars of similar type present an opportunity to isolate the effects of planets on host star abundances. Here we present a differential elemental abundance analysis of the XO-2 stellar binary, in which both G9 stars host giant planets, one of which is transiting. Building on our previous work, we report 16 elemental abundances and compare the $\Delta$(XO-2N-XO-S) values to elemental condensation temperatures. The $\Delta$(N-S) values and slopes with condensation temperature resulting from four different pairs of stellar parameters are compared to explore the effects of changing the relative temperature and gravity of the stars. We find that most of the abundance differences between the stars depend on the chosen stellar parameters, but that Fe, Si, and potentially Ni are consistently enhanced in XO-2N regardless of the chosen stellar parameters. This study emphasizes the power of binary host star abundance analysis for probing the effects of giant planet formation, but also illustrates the potentially large uncertainties in abundance differences and slopes induced by changes in stellar temperature and gravity.

Abundance Differences Between Exoplanet Binary Host Stars XO-2N and XO-2S -- Dependence on Stellar Parameters [Replacement]

The chemical composition of exoplanet host stars is an important factor in understanding the formation and characteristics of their orbiting planets. The best example of this to date is the planet-metallicity correlation. Other proposed correlations are thus far less robust, in part due to uncertainty in the chemical history of stars pre- and post-planet formation. Binary host stars of similar type present an opportunity to isolate the effects of planets on host star abundances. Here we present a differential elemental abundance analysis of the XO-2 stellar binary, in which both G9 stars host giant planets, one of which is transiting. Building on our previous work, we report 16 elemental abundances and compare the $\Delta$(XO-2N-XO-S) values to elemental condensation temperatures. The $\Delta$(N-S) values and slopes with condensation temperature resulting from four different pairs of stellar parameters are compared to explore the effects of changing the relative temperature and gravity of the stars. We find that most of the abundance differences between the stars depend on the chosen stellar parameters, but that Fe, Si, and potentially Ni are consistently enhanced in XO-2N regardless of the chosen stellar parameters. This study emphasizes the power of binary host star abundance analysis for probing the effects of giant planet formation, but also illustrates the potentially large uncertainties in abundance differences and slopes induced by changes in stellar temperature and gravity.

How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius [Replacement]

Precise and accurate parameters for late-type (late K and M) dwarf stars are important for characterization of any orbiting planets, but such determinations have been hampered by these stars’ complex spectra and dissimilarity to the Sun. We exploit an empirically calibrated method to estimate spectroscopic effective temperature ($T_{\rm{eff}}$) and the Stefan-Boltzmann law to determine radii of 183 nearby K7-M7 single stars with a precision of 2-5%. Our improved stellar parameters enable us to develop model-independent relations between $T_{\rm{eff}}$ or absolute magnitude and radius, as well as between color and $T_{\rm{eff}}$. The derived $T_{\rm{eff}}$-radius relation depends strongly on [Fe/H], as predicted by theory. The relation between absolute $K_S$ magnitude and radius can predict radii accurate to $\simeq$3%. We derive bolometric corrections to the $VR_CI_CgrizJHK_S$ and Gaia passbands as a function of color, accurate to 1-3%. We confront the reliability of predictions from Dartmouth stellar evolution models using a Markov Chain Monte Carlo to find the values of unobservable model parameters (mass, age) that best reproduce the observed effective temperature and bolometric flux while satisfying constraints on distance and metallicity as Bayesian priors. With the inferred masses we derive a semi-empirical mass-absolute magnitude relation with a scatter of 2% in mass. The best-agreement models over-predict stellar $T_{\rm{eff}}$s by an average of 2.2% and under-predict stellar radii by 4.6%, similar to differences with values from low-mass eclipsing binaries. These differences are not correlated with metallicity, mass, or indicators of activity, suggesting issues with the underlying model assumptions e.g., opacities or convective mixing length.

How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius [Replacement]

Precise and accurate parameters for late-type (late K and M) dwarf stars are important for characterization of any orbiting planets, but such determinations have been hampered by these stars’ complex spectra and dissimilarity to the Sun. We exploit an empirically calibrated method to estimate spectroscopic effective temperature ($T_{\rm{eff}}$) and the Stefan–Boltzmann law to determine radii of 183 nearby K7-M7 single stars with a precision of 2-5%. Our improved stellar parameters enable us to develop model-independent relations between $T_{\rm{eff}}$ or absolute magnitude and radius, as well as between color and $T_{\rm{eff}}$. The derived $T_{\rm{eff}}$–radius relation depends strongly on [Fe/H], as predicted by theory. The relation between absolute $K_S$ magnitude and radius can predict radii accurate to $\simeq$3%. We derive bolometric corrections to the $VR_CI_CgrizJHK_S$ and {\it Gaia} passbands as a function of color, accurate to 1-3%. We confront the reliability of predictions from Dartmouth stellar evolution models using a Markov Chain Monte Carlo to find the values of unobservable model parameters (mass, age) that best reproduce the observed effective temperature and bolometric flux while satisfying constraints on distance and metallicity as Bayesian priors. With the inferred masses we derive a semi-empirical mass–absolute magnitude relation with a scatter of 2% in mass. The best-agreement models over-predict stellar $T_{\rm{eff}}$s by an average of 2.2% and under-predict stellar radii by 4.6%, similar to differences with values from low-mass eclipsing binaries. These differences are not correlated with metallicity, mass, or indicators of activity, suggesting issues with the underlying model assumptions e.g., opacities or convective mixing length.

Solar analogs with and without planets: $T_C$ trends and galactic evolution

We explore a sample of 148 solar-like stars to search for a possible correlation between the slopes of the abundance trends versus condensation temperature (known as the Tc slope) both with stellar parameters and Galactic orbital parameters in order to understand the nature of the peculiar chemical signatures of these stars and the possible connection with planet formation. We find that the Tc slope correlates at a significant level with the stellar age and the stellar surface gravity. We also find tentative evidence that the Tc slope correlates with the mean galactocentric distance of the stars (Rmean), suggesting that stars that originated in the inner Galaxy have fewer refractory elements relative to the volatile ones. We found that the chemical peculiarities (small refractory-to-volatile ratio) of planet-hosting stars is probably a reflection of their older age and their inner Galaxy origin. We conclude that the stellar age and probably Galactic birth place are key to establish the abundances of some specific elements.

Solar analogs with and without planets: T$_c$ trends and galactic evolution [Replacement]

We explore a sample of 148 solar-like stars to search for a possible correlation between the slopes of the abundance trends versus condensation temperature (known as the Tc slope) both with stellar parameters and Galactic orbital parameters in order to understand the nature of the peculiar chemical signatures of these stars and the possible connection with planet formation. We find that the Tc slope correlates at a significant level with the stellar age and the stellar surface gravity. We also find tentative evidence that the Tc slope correlates with the mean galactocentric distance of the stars (Rmean), suggesting that stars that originated in the inner Galaxy have fewer refractory elements relative to the volatile ones. We found that the chemical peculiarities (small refractory-to-volatile ratio) of planet-hosting stars is probably a reflection of their older age and their inner Galaxy origin. We conclude that the stellar age and probably Galactic birth place are key to establish the abundances of some specific elements.

High Dispersion Spectroscopy of Solar-type Superflare Stars. II. Stellar Rotation, Starspots, and Chromospheric Activities

We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS. These 50 stars were selected from the solar-type superflare stars that we had discovered from the Kepler data. More than half (34 stars) of these 50 target superflare stars show no evidence of binarity, and we estimated stellar parameters of these 34 stars in our previous study (Notsu et al. 2015, hereafter called Paper I). According to our previous studies using Kepler data, superflare stars show quasi-periodic brightness variations whose amplitude (0.1-10\%) is much larger than that of the solar brightness variations (0.01-0.1\%) caused by the existence of sunspots on the rotating solar surface. In this study, we investigated whether these quasi-periodic brightness variations of superflare stars are explained by the rotation of a star with fairly large starspots, by using stellar parameters derived in Paper I. First, we confirmed that the value of the projected rotational velocity $v \sin i$ is consistent with the rotational velocity estimated from the period of the brightness variation. Next, we measured the intensity of Ca II infrared triplet lines and H$\alpha$ line, good indicators of the stellar chromospheric activity, and compared them with other stellar properties. The intensity of Ca II infrared triplet lines indicates that the mean magnetic field strength ($\langle fB\rangle$) of the target superflare stars can be higher than that of the Sun. A correlation between the amplitude of the brightness variation and the intensity of Ca II triplet line was found. All the targets expected to have large starspots because of their large amplitude of the brightness variation show high chromospheric activities compared to the Sun. These results support that the brightness variation of superflare stars is due to the rotation with large starspots.

High Dispersion Spectroscopy of Solar-type Superflare Stars. I. Temperature, Surface Gravity, Metallicity, and $v \sin i$

We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS, and measured the stellar parameters of them. These 50 targets were selected from the solar-type (G-type main sequence) superflare stars that we had discovered from the Kepler photometric data. As a result of these spectroscopic observations, we found that more than half (34 stars) of our 50 targets have no evidence of binary system. We then estimated effective temperature ($T_{\rm{eff}}$), surface gravity ($\log g$), metallicity ([Fe/H]), and projected rotational velocity ($v\sin i$) of these 34 superflare stars on the basis of our spectroscopic data. The accuracy of our estimations is higher than that of Kepler Input Catalog (KIC) values, and the differences between our values and KIC values ($(\Delta T_{\rm{eff}})_{\rm{rms}} \sim 219$K, $(\Delta \log g)_{\rm{rms}} \sim 0.37$ dex, and $(\Delta\rm{[Fe/H]})_{\rm{rms}} \sim 0.46$ dex) are comparable to the large uncertainties and systematic differences of KIC values reported by the previous researches. We confirmed that the estimated $T_{\rm{eff}}$ and $\log g$ values of the 34 superflare stars are roughly in the range of solar-type stars. In particular, these parameters and the brightness variation period ($P_{0}$) of 9 stars are in the range of "Sun-like" stars ($5600\leq T_{\rm{eff}}\leq 6000$K, $\log g\geq$4.0, and $P_{0}>$10 days). Five of the 34 target stars are fast rotators ($v \sin i \geq 10$km s$^{-1}$), while 22 stars have relatively low $v \sin i$ values ($v \sin i<5$km s$^{-1}$). These results suggest that stars whose spectroscopic properties similar to the Sun can have superflares, and this supports the hypothesis that the Sun might cause a superflare.

High Dispersion Spectroscopy of Solar-type Superflare Stars. I. Temperature, Surface Gravity, Metallicity, and $v \sin i$ [Replacement]

We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS, and measured the stellar parameters of them. These 50 targets were selected from the solar-type (G-type main sequence) superflare stars that we had discovered from the Kepler photometric data. As a result of these spectroscopic observations, we found that more than half (34 stars) of our 50 targets have no evidence of binary system. We then estimated effective temperature ($T_{\rm{eff}}$), surface gravity ($\log g$), metallicity ([Fe/H]), and projected rotational velocity ($v\sin i$) of these 34 superflare stars on the basis of our spectroscopic data. The accuracy of our estimations is higher than that of Kepler Input Catalog (KIC) values, and the differences between our values and KIC values ($(\Delta T_{\rm{eff}})_{\rm{rms}} \sim 219$K, $(\Delta \log g)_{\rm{rms}} \sim 0.37$ dex, and $(\Delta\rm{[Fe/H]})_{\rm{rms}} \sim 0.46$ dex) are comparable to the large uncertainties and systematic differences of KIC values reported by the previous researches. We confirmed that the estimated $T_{\rm{eff}}$ and $\log g$ values of the 34 superflare stars are roughly in the range of solar-type stars. In particular, these parameters and the brightness variation period ($P_{0}$) of 9 stars are in the range of "Sun-like" stars ($5600\leq T_{\rm{eff}}\leq 6000$K, $\log g\geq$4.0, and $P_{0}>$10 days). Five of the 34 target stars are fast rotators ($v \sin i \geq 10$km s$^{-1}$), while 22 stars have relatively low $v \sin i$ values ($v \sin i<5$km s$^{-1}$). These results suggest that stars whose spectroscopic properties similar to the Sun can have superflares, and this supports the hypothesis that the Sun might cause a superflare.

The LAMOST Stellar Parameter Pipeline at Peking University --- LSP3

We introduce the LAMOST Stellar Parameter Pipeline at Peking University — LSP3, developed and implemented for the determinations of radial velocity $V_{\rm r}$ and stellar atmospheric parameters (effective temperature $T_{\rm eff}$, surface gravity log\,$g$, metallicity [Fe/H]) for the LAMOST Spectroscopic Survey of the Galactic Anti-center (LSS-GAC). We describe the algorithms of LSP3 and examine the accuracy of parameters yielded by it. The precision and accuracy of parameters yielded are investigated by comparing results of multi-epoch observations and of candidate members of open and globular clusters, with photometric calibration, as well as with independent determinations available from a number of external databases, including the PASTEL archive, the APOGEE, SDSS and RAVE surveys, as well as those released in the LAMOST DR1. The uncertainties of LSP3 parameters are characterized and quantified as a function of the spectral signal-to-noise ratio (SNR) and stellar atmospheric parameters. We conclude that the current implementation of LSP3 has achieved an accuracy of 5.0\,km\,s$^{-1}$, 150\,K, 0.25\,dex, 0.15\,dex for the radial velocity, effective temperature, surface gravity and metallicity, respectively, for LSS-GAC spectra of FGK stars of SNRs per pixel higher than 10. The LSP3 has been applied to over a million LSS-GAC spectra collected hitherto. Stellar parameters yielded by the LSP3 will be released to the general public following the data policy of LAMOST, together with estimates of the interstellar extinction $E(B-V)$ and stellar distances, deduced by combining spectroscopic and multi-band photometric measurements using a variety of techniques.

Stellar Parameters for HD 69830, a Nearby Star with Three Neptune Mass Planets and an Asteroid Belt

We used the CHARA Array to directly measure the angular diameter of HD 69830, home to three Neptune mass planets and an asteroid belt. Our measurement of 0.674+/-0.014 milli-arcseconds for the limb-darkened angular diameter of this star leads to a physical radius of R$_*$ = 0.9058$\pm$0.0190 R\sun and luminosity of L* = 0.622+/-0.014 Lsun when combined with a fit to the spectral energy distribution of the star. Placing these observed values on an Hertzsprung-Russel (HR) diagram along with stellar evolution isochrones produces an age of 10.6+/-4 Gyr and mass of 0.863$\pm$0.043 M\sun. We use archival optical echelle spectra of HD 69830 along with an iterative spectral fitting technique to measure the iron abundance ([Fe/H]=-0.04+/-0.03), effective temperature (5385+/-44 K) and surface gravity (log g = 4.49+/-0.06). We use these new values for the temperature and luminosity to calculate a more precise age of 7.5+/-Gyr. Applying the values of stellar luminosity and radius to recent models on the optimistic location of the habitable zone produces a range of 0.61-1.44 AU; partially outside the orbit of the furthest known planet (d) around HD 69830. Finally, we estimate the snow line at a distance of 1.95+/-0.19 AU, which is outside the orbit of all three planets and its asteroid belt.

Quest for finding the lost siblings of the Sun

The aim of this paper is to find lost siblings of the Sun by analyzing high resolution spectra. Finding solar siblings will enable us to constrain the parameters of the parental cluster and the birth place of the Sun in the Galaxy. The solar siblings can be identified by accurate measurements of metallicity, stellar age and elemental abundances for solar neighbourhood stars. The solar siblings candidates were kinematically selected based on their proper motions, parallaxes and colours. Stellar parameters were determined through a purely spectroscopic approach and partly physical method, respectively. Comparing synthetic with observed spectra, elemental abundances were computed based on the stellar parameters obtained using a partly physical method. A chemical tagging technique was used to identify the solar siblings. We present stellar parameters, stellar ages, and detailed elemental abundances for Na, Mg, Al, Si, Ca, Ti, Cr, Fe, and Ni for 32 solar sibling candidates. Our abundances analysis shows that four stars are chemically homogenous together with the Sun. Technique of chemical tagging gives us a high probability that they might be from the same open cluster. Only one candidate HIP 40317 which has solar metallicity and age could be a solar sibling. We performed simulations of the Sun’s birth cluster in analytical Galactic model and found that most of the radial velocities of the solar siblings lie in the range $-10 \leq \mathrm{V_r}\leq 10$ $\mathrm{km~s^{-1}}$, which is smaller than the radial velocity of HIP 40317 $(\mathrm{V_r} = 34.2~\mathrm{km~s^{-1}})$, under different Galactic parameters and different initial conditions of the Sun’s birth cluster. The sibling status for HIP 40317 is not directly supported by our dynamical analysis.

Bayesian Analysis for Stellar Evolution with Nine Parameters (BASE-9): User's Manual

BASE-9 is a Bayesian software suite that recovers star cluster and stellar parameters from photometry. BASE-9 is useful for analyzing single-age, single-metallicity star clusters, binaries, or single stars, and for simulating such systems. BASE-9 uses Markov chain Monte Carlo and brute-force numerical integration techniques to estimate the posterior probability distributions for the age, metallicity, helium abundance, distance modulus, and line-of-sight absorption for a cluster, and the mass, binary mass ratio, and cluster membership probability for every stellar object. BASE-9 is provided as open source code on a version-controlled web server. The executables are also available as Amazon Elastic Compute Cloud images. This manual provides potential users with an overview of BASE-9, including instructions for installation and use.

The SAGA so far: reading the history of the Galaxy with asteroseismology

Asteroseismology has the capability of delivering stellar properties which would otherwise be inaccessible, such as radii, masses and thus ages of stars. When this information is coupled with classical determinations of stellar parameters, such as metallicities, effective temperatures and angular diameters, powerful new diagnostics for stellar and Galactic studies can be obtained. The ongoing Stroemgren survey for Asteroseismology and Galactic Archaeology (SAGA) is pursuing such a goal, by determining photometric stellar parameters for stars with seismic oscillations measured by the Kepler satellite. As the survey continues and expands in sample size, SAGA will provide an unprecedented opportunity to constrain theories of the evolution of the Milky Way disc.

A Machine Learning Method to Infer Fundamental Stellar Parameters from Photometric Light Curves

A fundamental challenge for wide-field imaging surveys is obtaining follow-up spectroscopic observations: there are > $10^9$ photometrically cataloged sources, yet modern spectroscopic surveys are limited to ~few x $10^6$ targets. As we approach the Large Synoptic Survey Telescope (LSST) era, new algorithmic solutions are required to cope with the data deluge. Here we report the development of a machine-learning framework capable of inferring fundamental stellar parameters (Teff, log g, and [Fe/H]) using photometric-brightness variations and color alone. A training set is constructed from a systematic spectroscopic survey of variables with Hectospec/MMT. In sum, the training set includes ~9000 spectra, for which stellar parameters are measured using the SEGUE Stellar Parameters Pipeline (SSPP). We employed the random forest algorithm to perform a non-parametric regression that predicts Teff, log g, and [Fe/H] from photometric time-domain observations. Our final, optimized model produces a cross-validated root-mean-square error (RMSE) of 165 K, 0.39 dex, and 0.33 dex for Teff, log g, and [Fe/H], respectively. Examining the subset of sources for which the SSPP measurements are most reliable, the RMSE reduces to 125 K, 0.37 dex, and 0.27 dex, respectively, comparable to what is achievable via low-resolution spectroscopy. For variable stars this represents a ~12-20% improvement in RMSE relative to models trained with single-epoch photometric colors. As an application of our method, we estimate stellar parameters for ~54,000 known variables. We argue that this method may convert photometric time-domain surveys into pseudo-spectrographic engines, enabling the construction of extremely detailed maps of the Milky Way, its structure, and history.

Stars with and without planets: Where do they come from?

A long and thorough investigation of chemical abundances of planet-hosting stars that lasted for more than a decade has finally beared fruit. We explore a sample of 148 solar-like stars to search for a possible correlation between the slopes of the abundance trends versus condensation temperature (known as the Tc slope) both with stellar parameters and Galactic orbital parameters in order to understand the nature of the peculiar chemical signatures of these stars and the possible connection with planet formation. We find that the Tc slope correlates at a significant level (at more than 4sigma) with the stellar age and the stellar surface gravity. We also find tentative evidence that the Tc slope correlates with the mean galactocentric distance of the stars (Rmean), suggesting that stars that originated in the inner Galaxy have fewer refractory elements relative to the volatile ones. We found that the chemical peculiarities (small refractory-to-volatile ratio) of planet-hosting stars is merely a reflection of their older age and their inner Galaxy origin. We conclude that the stellar age and probably Galactic birth place are key to establish the abundances of some specific elements.

Stellar parameters and chemical abundances of 223 evolved stars with and without planets

We present fundamental stellar parameters and chemical abundances for a sample of 86 evolved stars with planets and for a control sample of 137 stars without planets. The analysis was based on both high S/N and resolution echelle spectra. The goals of this work are i) to investigate chemical differences between stars with and without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. In agreement with previous studies, we find that subgiants with planets are, on average, more metal-rich than subgiants without planets by ~ 0.16 dex. The [Fe/H] distribution of giants with planets is centered at slightly subsolar metallicities and there is no metallicity enhancement relative to the [Fe/H] distribution of giants without planets. Furthermore, contrary to recent results, we do not find any clear difference between the metallicity distributions of stars with and without planets for giants with M > 1.5 Msun. With regard to the other chemical elements, the analysis of the [X/Fe] distributions shows differences between giants with and without planets for some elements, particularly V, Co, and Ba. Analyzing the planet properties, some interesting trends might be emerging: i) multi-planet systems around evolved stars show a slight metallicity enhancement compared with single-planet systems; ii) planets with a $\lesssim$ 0.5 AU orbit subgiants with [Fe/H] > 0 and giants hosting planets with a $\lesssim$ 1 AU have [Fe/H] < 0; iii) higher-mass planets tend to orbit more metal-poor giants with M < 1.5 Msun, whereas planets around subgiants seem to follow the planet-mass metallicity trend observed on dwarf hosts; iv) planets orbiting giants show lower orbital eccentricities than those orbiting subgiants and dwarfs.

Stellar parameters and chemical abundances of 223 evolved stars with and without planets [Replacement]

We present fundamental stellar parameters and chemical abundances for a sample of 86 evolved stars with planets and for a control sample of 137 stars without planets. The analysis was based on both high S/N and resolution echelle spectra. The goals of this work are i) to investigate chemical differences between stars with and without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. In agreement with previous studies, we find that subgiants with planets are, on average, more metal-rich than subgiants without planets by ~ 0.16 dex. The [Fe/H] distribution of giants with planets is centered at slightly subsolar metallicities and there is no metallicity enhancement relative to the [Fe/H] distribution of giants without planets. Furthermore, contrary to recent results, we do not find any clear difference between the metallicity distributions of stars with and without planets for giants with M > 1.5 Msun. With regard to the other chemical elements, the analysis of the [X/Fe] distributions shows differences between giants with and without planets for some elements, particularly V, Co, and Ba. Analyzing the planet properties, some interesting trends might be emerging: i) multi-planet systems around evolved stars show a slight metallicity enhancement compared with single-planet systems; ii) planets with a $\lesssim$ 0.5 AU orbit subgiants with [Fe/H] > 0 and giants hosting planets with a $\lesssim$ 1 AU have [Fe/H] < 0; iii) higher-mass planets tend to orbit more metal-poor giants with M < 1.5 Msun, whereas planets around subgiants seem to follow the planet-mass metallicity trend observed on dwarf hosts; iv) planets orbiting giants show lower orbital eccentricities than those orbiting subgiants and dwarfs.

Stellar parameters and chemical abundances of 223 evolved stars with and without planets [Replacement]

We present fundamental stellar parameters and chemical abundances for a sample of 86 evolved stars with planets and for a control sample of 137 stars without planets. The analysis was based on both high S/N and resolution echelle spectra. The goals of this work are i) to investigate chemical differences between stars with and without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. In agreement with previous studies, we find that subgiants with planets are, on average, more metal-rich than subgiants without planets by ~ 0.16 dex. The [Fe/H] distribution of giants with planets is centered at slightly subsolar metallicities and there is no metallicity enhancement relative to the [Fe/H] distribution of giants without planets. Furthermore, contrary to recent results, we do not find any clear difference between the metallicity distributions of stars with and without planets for giants with M > 1.5 Msun. With regard to the other chemical elements, the analysis of the [X/Fe] distributions shows differences between giants with and without planets for some elements, particularly V, Co, and Ba. Analyzing the planet properties, some interesting trends might be emerging: i) multi-planet systems around evolved stars show a slight metallicity enhancement compared with single-planet systems; ii) planets with a $\lesssim$ 0.5 AU orbit subgiants with [Fe/H] > 0 and giants hosting planets with a $\lesssim$ 1 AU have [Fe/H] < 0; iii) higher-mass planets tend to orbit more metal-poor giants with M < 1.5 Msun, whereas planets around subgiants seem to follow the planet-mass metallicity trend observed on dwarf hosts; iv) planets orbiting giants show lower orbital eccentricities than those orbiting subgiants and dwarfs.

MY Camelopardalis, a very massive merger progenitor

Context. The early-type binary MY Cam belongs to the young open cluster Alicante 1, embedded in Cam OB3. Aims. MY Cam consists of two early-O type main-sequence stars and shows a photometric modulation suggesting an orbital period slightly above one day. We intend to confirm this orbital period and derive orbital and stellar parameters. Methods. Timing analysis of a very exhaustive (4607 points) light curve indicates a period of 1.1754514 +- 0.0000015 d. High- resolution spectra and the cross-correlation technique implemented in the TODCOR program were used to derive radial velocities and obtain the corresponding radial velocity curves for MY Cam. Modelling with the stellar atmosphere code FASTWIND was used to obtain stellar parameters and create templates for cross-correlation. Stellar and orbital parameters were derived using the Wilson-Devinney code, such that a complete solution to the binary system could be described. Results. The determined masses of the primary and secondary stars in MY Cam are 37.7 +- 1.6 and 31.6 +- 1.4 Msol, respectively. The corresponding temperatures, derived from the model atmosphere fit, are 42 000 and 39 000 K, with the more massive component being hotter. Both stars are overfilling their Roche lobes, sharing a common envelope. Conclusions. MY Cam contains the most massive dwarf O-type stars found so far in an eclipsing binary. Both components are still on the main sequence, and probably not far from the zero-age main sequence. The system is a likely merger progenitor, owing to its very short period.

Correcting the spectroscopic surface gravity using transits and asteroseismology. No significant effect on temperatures or metallicities with ARES+MOOG in LTE

Precise stellar parameters are crucial for several reasons, amongst which are the precise characterization of orbiting exoplanets and the correct determination of galactic chemical evolution. The atmospheric parameters are extremely important because all the other stellar parameters depend on them. Using our standard equivalent-width method on high-resolution spectroscopy, good precision can be obtained for the derived effective temperature and metallicity. The surface gravity, however, is usually not well constrained with spectroscopy. We use two different samples of FGK dwarfs to study the effect of the stellar surface gravity on the precise spectroscopic determination of the other atmospheric parameters. Furthermore, we present a straightforward formula for correcting the spectroscopic surface gravities derived by our method and with our linelists. Our spectroscopic analysis is based on Kurucz models in LTE, performed with the MOOG code to derive the atmospheric parameters. The surface gravity was either left free or fixed to a predetermined value. The latter is either obtained through a photometric transit light curve or derived using asteroseismology. We find first that, despite some minor trends, the effective temperatures and metallicities for FGK dwarfs derived with the described method and linelists are, in most cases, only affected within the errorbars by using different values for the surface gravity, even for very large differences in surface gravity, so they can be trusted. The temperatures derived with a fixed surface gravity continue to be compatible within 1 sigma with the accurate results of the InfraRed Flux Method (IRFM), as is the case for the unconstrained temperatures. Secondly, we find that the spectroscopic surface gravity can easily be corrected to a more accurate value using a linear function with the effective temperature.

Correcting the spectroscopic surface gravity using transits and asteroseismology. No significant effect on temperatures or metallicities with ARES+MOOG in LTE [Replacement]

Precise stellar parameters are crucial for several reasons, amongst which are the precise characterization of orbiting exoplanets and the correct determination of galactic chemical evolution. The atmospheric parameters are extremely important because all the other stellar parameters depend on them. Using our standard equivalent-width method on high-resolution spectroscopy, good precision can be obtained for the derived effective temperature and metallicity. The surface gravity, however, is usually not well constrained with spectroscopy. We use two different samples of FGK dwarfs to study the effect of the stellar surface gravity on the precise spectroscopic determination of the other atmospheric parameters. Furthermore, we present a straightforward formula for correcting the spectroscopic surface gravities derived by our method and with our linelists. Our spectroscopic analysis is based on Kurucz models in LTE, performed with the MOOG code to derive the atmospheric parameters. The surface gravity was either left free or fixed to a predetermined value. The latter is either obtained through a photometric transit light curve or derived using asteroseismology. We find first that, despite some minor trends, the effective temperatures and metallicities for FGK dwarfs derived with the described method and linelists are, in most cases, only affected within the errorbars by using different values for the surface gravity, even for very large differences in surface gravity, so they can be trusted. The temperatures derived with a fixed surface gravity continue to be compatible within 1 sigma with the accurate results of the InfraRed Flux Method (IRFM), as is the case for the unconstrained temperatures. Secondly, we find that the spectroscopic surface gravity can easily be corrected to a more accurate value using a linear function with the effective temperature.

FORS2/VLT survey of Milky Way globular clusters I. Description of the method for derivation of metal abundances in the optical and application to NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and Terzan 8

(abridged) We have observed almost 1/3 of the globular clusters in the Milky Way, targeting distant and/or highly reddened objects, besides a few reference clusters. A large sample of red giant stars was observed with FORS2@VLT/ESO at R ~ 2,000. The method for derivation of stellar parameters is presented with application to six reference clusters. We aim at deriving the stellar parameters effective temperature, gravity, metallicity and alpha-element enhancement, as well as radial velocity, for membership confirmation of individual stars in each cluster. We analyse the spectra collected for the reference globular clusters NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426 and Terzan 8. They cover the full range of globular cluster metallicities, and are located in the bulge, disc and halo. Full spectrum fitting techniques are applied, by comparing each target spectrum with a stellar library in the optical region at 4560-5860 A. We employed the library of observed spectra MILES, and the synthetic library by Coelho et al. (2005). Validation of the method is achieved through recovery of the known atmospheric parameters for 49 well-studied stars that cover a wide range in the parameter space. We adopted as final stellar parameters (effective temperatures, gravities, metallicities) the average of results using MILES and Coelho et al. libraries. We identified 4 member stars in NGC 6528, 13 in NGC 6553, 10 in M 71, 5 in NGC 6558, 5 in NGC 6426 and 12 in Terzan 8. Radial velocities, Teff, log(g), [Fe/H] and alpha-element enhancements were derived. We derived abundances for NGC 6426 from spectroscopy for the first time. The method proved to be reliable for red giant stars observed with resolution R ~ 2,000, yielding results compatible with high-resolution spectroscopy. The derived alpha-element abundances show [A/Fe] vs. [Fe/H] consistent with that of field stars at the same metallicities.

Photometric stellar parameters for asteroseismology and Galactic studies

Asteroseismology has the capability of delivering stellar properties which would otherwise be inaccessible, such as radii, masses and thus ages of stars. When coupling this information with classical determinations of stellar parameters, such as metallicities, effective temperatures and angular diameters, powerful new diagnostics for both stellar and Galactic studies can be obtained. I review how different photometric systems and filters carry important information on classical stellar parameters, the accuracy at which those parameters can be derived, and summarize some of the calibrations available in the literature for late-type stars. Recent efforts in combining classical and asteroseismic parameters are discussed, and the unique- ness of their intertwine is highlighted.

 

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