- ID:
- ivo://CDS.VizieR/J/AJ/158/56
- Title:
- Stellar parameters of M and K dwarfs
- Short Name:
- J/AJ/158/56
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Empirical correlations between stellar parameters such as rotation or radius and magnetic activity diagnostics require estimates of the effective temperatures and the stellar radii. The aim of this study is to propose simple methods that can be applied to large samples of stars in order to derive estimates of the stellar parameters. Good empirical correlations between red/infrared colors (e.g., (R-I)_C_) and effective temperatures have been well established for a long time. The more recent (R-I)_C_ color-T_eff_ correlation using the data of Mann et al. (2015, J/ApJ/804/64, hereafter M15) and Boyajian et al. (2012, J/ApJ/757/112, hereafter B12) shows that this color can be applied as a temperature estimate for large samples of stars. We find that the mean scatter in T_eff_ relative to the (R-I)_C_-T_eff_ relationship of B12 and M15 data is only +/-3{sigma}=44.6 K for K dwarfs and +/-3{sigma}=39.4 K for M dwarfs. These figures are small and show that the (R-I)_C_ color can be used as a first-guess effective temperature estimator for K and M dwarfs. We derive effective temperatures for about 1910 K and M dwarfs using the calibration of (R-I)_C_ color-T_eff_ from B12 and M15 data. We also compiled T_eff_ and metallicity measurements available in the literature using the VizieR database. We determine T_eff_ for 441 stars with previously unknown effective temperatures. We also identified 21 new spectroscopic binaries and one triple system from our high-resolution spectra.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/II/237
- Title:
- Stellar Photometry in Johnson's 11-color system
- Short Name:
- II/237
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue gives photometric data in the UBVRIJHKLMN colors and some additional information. Data for the JHKLMN bands come from NASA Ref. Pub. 1294 (1993). More complete information is found in Wisconsin Astrophysics 504 (1993) The effective wavelength of the Johsnon filters are: U = 360 nm B = 450 nm V = 555 nm R = 670 nm I = 870 nm J = 1.2 um H = 1.62um K = 2.2 um L = 3.5 um M = 5.0 um N = 9.0 um
- ID:
- ivo://CDS.VizieR/J/A+A/568/A119
- Title:
- Stellar physical parameters for young stars
- Short Name:
- J/A+A/568/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A uvbyH{beta} Stromgren photometric survey covering 16 square degrees in the anticenter direction was carried out using the Wide Field Camera at the Isaac Newton Telescope. Physical parameters like stellar distances and extinctions for the young stars of our survey are presented here. We developed a new method for deriving physical parameters from Stromgren photometry and also implemented and tested it. This is a model-based method that uses the most recent available stellar atmospheric models and evolutionary tracks to interpolate in a 3D grid of the unreddened indexes [m1], [c1] and H{beta}. Distances derived from both this method and the classical pre-Hipparcos calibrations were tested against Hipparcos parallaxes and found to be accurate. Furthermore, a shift in the atmospheric grids in the range Teff=[7000,9000]K was detected and a correction is proposed. The two methods were used to compute distances and reddening for around 12000 OBA-type stars in our Stromgren anticenter survey. Data from the IPHAS and 2MASS catalogs were used to complement the detection of emission line stars and to break the degeneracy between early and late photometric regions. We note that photometric distances can differ by more than 20%, those derived from the empirical calibrations being smaller than those derived with the new method, which agree better with the Hipparcos data.
- ID:
- ivo://CDS.VizieR/J/A+A/474/1081
- Title:
- Stellar population gradients in bulges. I
- Short Name:
- J/A+A/474/1081
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first paper presenting our long-term project aimed at studying the nature of bulges through analyzing their stellar population gradients. We present deep spectroscopic observations along the minor axis and the data reduction for a sample of 32 bulges of edge-on spiral galaxies. We explain in detail our procedures for measuring their dynamical parameters (rotation curves and velocity dispersion profiles) and line-strength indices, including the conversion to the Lick/IDS system. Tables giving the values of the dynamical parameters and line-strength indices at each galactocentric radius are presented (in electronic form) for each galaxy of the sample. The derived line-strength gradients from this dataset will be analyzed in a forthcoming paper to set constraints on the different scenarios for the formation of the bulges.
- ID:
- ivo://CDS.VizieR/J/ApJS/173/104
- Title:
- Stellar population in Chamaeleon I
- Short Name:
- J/ApJS/173/104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present a new census of the stellar population in the ChamaeleonI star-forming region. Using optical and near-IR photometry and follow-up spectroscopy, I have discovered 50 new members of ChamaeleonI, expanding the census of known members to 226 objects. Fourteen of these new members have spectral types later than M6, which doubles the number of known members that are likely to be substellar. I have estimated extinctions, luminosities, and effective temperatures for the known members, used these data to construct an H-R diagram for the cluster, and inferred individual masses and ages with the theoretical evolutionary models of Baraffe and Chabrier. The low-mass stars are more widely distributed than members at other masses in the northern subcluster, but this is not the case in the southern subcluster. Meanwhile, the brown dwarfs have the same spatial distribution as the stars out to a radius of 3{deg} (8.5pc) from the center of ChamaeleonI.
- ID:
- ivo://CDS.VizieR/J/AJ/161/288
- Title:
- Stellar population in M53
- Short Name:
- J/AJ/161/288
- Date:
- 18 Jan 2022
- Publisher:
- CDS
- Description:
- We present results from a study of 94 red giant stars in the globular cluster M53. We use low-resolution spectra to measure the strength of CN and CH features at ~3800 and 4300{AA}, respectively. The strengths of these features are used to classify stars into a CN-enhanced and CN-normal population and to measure C and N abundances in all 94 stars. We find the red giant branch stars to be evenly split between the two populations identified, and observe the presence of CN-enhanced stars on the asymptotic giant branch. In addition, we identify five CH star candidates based on the strength of their CN and CH band features, and the presence of a P-branch in their CH band. We compare our identification of multiple populations to those based on the Na-O anticorrelation and pseudo-color indices in Hubble Space Telescope UV photometry, and find general agreement between all three methods. Our large sample size also allows us to study the radial distribution of each population, and we find that the CN-enhanced population is more centrally concentrated. We use our C and N measurements to compare the evolutionary changes in these elements as a function of magnitude between the two populations, and show that both populations experience similar evolutionary changes to the surface abundances of C and N. Finally, we calculate C+N+O abundances for each population and compare them to similar measurements made in M10; we find that in both clusters, CN-enhanced stars have a slightly enhanced C+N+O ({Delta}(C+N+O)~0.2dex).
- ID:
- ivo://CDS.VizieR/J/AJ/154/87
- Title:
- Stellar population of the young star cluster NGC 6231
- Short Name:
- J/AJ/154/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6231 is a young cluster (age ~2-7 Myr) dominating the Sco OB1 association (distance ~1.59 kpc) with ~100 O and B stars and a large pre-main-sequence stellar population. We combine a reanalysis of archival Chandra X-ray data with multiepoch near-infrared (NIR) photometry from the VISTA Variables in the Via Lactea (VVV) survey and published optical catalogs to obtain a catalog of 2148 probable cluster members. This catalog is 70% larger than previous censuses of probable cluster members in NGC 6231. It includes many low-mass stars detected in the NIR but not in the optical and some B stars without previously noted X-ray counterparts. In addition, we identify 295 NIR variables, about half of which are expected to be pre-main-sequence stars. With the more complete sample, we estimate a total population in the Chandra field of 5700-7500 cluster members down to 0.08 M_{sun}_ (assuming a universal initial mass function) with a completeness limit at 0.5 M_{sun}_. A decrease in stellar X-ray luminosities is noted relative to other younger clusters. However, within the cluster, there is little variation in the distribution of X-ray luminosities for ages less than 5 Myr. The X-ray spectral hardness for B stars may be useful for distinguishing between early-B stars with X-rays generated in stellar winds and B-star systems with X-rays from a pre-main-sequence companion (>35% of B stars). A small fraction of catalog members have unusually high X-ray median energies or reddened NIR colors, which might be explained by absorption from thick or edge-on disks or being background field stars.
- ID:
- ivo://CDS.VizieR/J/A+A/649/A93
- Title:
- Stellar populations of NGC 3311
- Short Name:
- J/A+A/649/A93
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Massive early-type galaxies are believed to be the end result of an extended mass accretion history. The stars formed in situ, very early during the initial phase of the assembly, might have originated from an extremely intense and rapid burst of star formation. These stars may still be found within the cores of such galaxies at z=0, depending on their accretion and merger histories. We wish to investigate the presence of a surviving high-z compact progenitor component in the brightest galaxy of the Hydra~I cluster, NGC~3311, by mapping its 2D kinematics and stellar population out to 2 effective radii. Our goal is to understand the formation of its several structural components and trace their mass assembly back in time. We combine MUSE observations, a customized and extended version of the state-of-the-art EMILES single stellar population models, and a newly developed parametric fully Bayesian framework to model the observed spectra using full-spectrum fitting. We present 2D maps, as well as radial profiles, of the stellar velocity dispersion, age, total metallicity, {alpha}-element, sodium abundance ([Na/Fe]), and the initial mass function slope. All properties have significant gradients, confirming the existence of multiple structural components, also including a "blue spot" characterized by younger and metal-richer stars. We find that the component dominating the light budget of NGC 3311 within R<2.0kpc, is the surviving z=0 analogue of a high-z compact core, according to the definition of Pulsoni et al. (2021). This concentrated structure has a relatively small velocity dispersion (sigma~180km/s), is very old (ages~11Gyr), metal-rich ([Z/H]~0.2 and [Na/Fe]~0.4), and has a bottom-heavy IMF (with slope Gamma_b_~2.4). In the outer region, instead, the line-of-sight velocity distribution becomes increasingly broader, and the stars have younger age. They are also metal and sodium poorer but {alpha}-element richer. The low-mass end of the IMF slope becomes Chabrier-like with increasing galactocentric distances. The existence of multiple structural components in NGC 3311 from photometry, kinematics, and stellar populations confirms the predictions from the two-phase formation scenario for NGC 3311, according to which a first very short, high-z star formation episode formed a compact stellar structure in its core, which then grew in size by the extended mass assembly of relatively massive satellites. Interestingly, the outer stellar population has an overabundant [alpha/Fe], most likely because NGC 3311, located at the center of the galaxy cluster, accreted stars from rapidly quenched satellites.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A139
- Title:
- Stellar populations of NGC 3311
- Short Name:
- J/A+A/589/A139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The history of the mass assembly of brightest cluster galaxies may be studied by mapping the stellar populations at large radial distances from the galaxy centre, where the dynamical times are long and preserve the chemodynamical signatures of the accretion events. To provide extended and robust measurements of the stellar population parameters in NGC 3311, the cD galaxy at the centre of the Hydra I cluster, and out to three effective radius. We wish to characterise the processes that drove the build up of the stellar light at all these radii. We obtained the spectra from several regions in NGC 3311 covering an area of ~3arcmin^2^ in the wavelength range 4800<lambda({AA})<5800, using the FORS2 spectrograph at the Very Large Telescope in the MXU mode. We measured the equivalent width of seven absorption-features defined in the Lick/IDS system, which were modelled by single stellar populations, to provide luminosity-weighted ages, metallicities, and alpha element abundances. The trends in the Lick indices and the distribution of the stellar population parameters indicate that the stars of NGC3311 may be divided in two radial regimes, one within and the another beyond one effective radius, R_e_=8.4kpc, similar to the distinction between the inner galaxy and the external halo derived from the NGC3311 velocity dispersion profile. The inner galaxy (R<R_e_) is old (age ~14Gyr), has negative metallicity gradients and positive alpha element gradients. The external halo is also very old, but has a negative age gradient. The metal and element abundances of the external halo both have a large scatter, indicating that stars from a variety of satellites with different masses have been accreted. The region in the extended halo associated with the off-centred envelope at 0<P.A.({deg})<90 (Arnaboldi et al., 2012A&A...545A..37A) has higher metallicity with respect to the symmetric external halo. The different stellar populations in the inner galaxy and extended halo reflect the dominance of in situ stars in the former and the accreted origin for the large majority of the stars in the latter. The low value of the velocity dispersion in the inner galaxy indicates that its stars are bound to the galaxy's gravitational potential, and the abundances and gradients suggest that the inner galaxy is formed in an outside-in scenario of merging gas-rich lumps, reminiscent of the first phase of galaxy formation. The external halo has a higher velocity dispersion, it is dynamically hotter than the galaxy and its stars are gravitationally driven by the cluster's gravitational potential. The stars in the external halo were removed from their parent galaxies, either disks with truncated star formation, or the outer regions of early-type galaxies. Late mass accretion at large radii is now coming from the tidal stripping of stars from dwarfs and S0 galaxies. These results provide supporting evidence for the recent theoretical models of formation of massive ellipticals as a two-phase process.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A148
- Title:
- Stellar populations towards Orion with Gaia DR1
- Short Name:
- J/A+A/608/A148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we use the first data release of the Gaia mission to explore the three-dimensional arrangement and age ordering of the many stellar groups toward the Orion OB association, aiming at a new classification and characterization of the stellar population not embedded in the Orion A and B molecular clouds. We make use of the parallaxes and proper motions provided in the Tycho Gaia Astrometric Solution (TGAS) subset of the Gaia Data Release 1 (DR1) catalog and of the combination of Gaia DR1 and 2MASS photometry. In TGAS, we find evidence for the presence of a young population at a parallax {varpi}~2.65mas, which is loosely distributed around the following known clusters: 25 Ori, {epsilon} Ori, and {sigma} Ori, and NGC 1980 ({iota} Ori) and the Orion Nebula Cluster (ONC). The low mass counterpart of this population is visible in the color magnitude diagrams constructed by combining Gaia DR1 G-band photometry and 2MASS. We study the density distribution of the young sources in the sky using a kernel density estimation (KDE). We find the same groups as in TGAS and also some other density enhancements that might be related to the recently discovered Orion X group, Orion dust ring, and {lambda} Ori complex. The maps also suggest that the 25 Ori group presents a northern elongation.We estimated the ages of this population using a Bayesian isochronal fitting procedure assuming a unique parallax value for all the sources, and we inferred the presence of an age gradient going from 25 Ori (13-15Myr) to the ONC (1-2Myr). We confirmed this age ordering by repeating the Bayesian fit using the Pan-STARRS1 data. Intriguingly, the estimated ages toward the NGC 1980 cluster span a broad range of values. This can either be due to the presence of two populations coming from two different episodes of star formation or to a large spread along the line of sight of the same population. Some confusion might arise from the presence of unresolved binaries, which are not modeled in the fit, and usually mimic a younger population. Finally, we provisionally relate the stellar groups to the gas and dust features in Orion. Our results form the first step toward using Gaia data to unravel the complex star formation history of the Orion region in terms of the various star formation episodes, their duration, and their effects on the surrounding interstellar medium.
