- ID:
- ivo://CDS.VizieR/J/MNRAS/487/5922
- Title:
- CP stars catalog (roAp, He-weak, He-rich)
- Short Name:
- J/MNRAS/487/5922
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To enlarge our data base of chemically peculiar stars, we compiled published data concerning the He-weak and He-rich stars observed by high-resolution spectroscopy techniques during last decades. Twenty He-weak and 28 He-rich stars have been added to the data base. We have also distinguished roAp stars from stars previously identified as Ap stars. To deepen our knowledge on statistical overview of the abundance anomalies versus the physical parameters of stars, we compared our data with previous compilations. We applied statistical tests on our data and found interesting correlations for effective temperature and surface gravity for all type of stars and a few correlations for projected rotation velocity only for He-rich stars. Because of the lack of the data, we could not check whether being a member of binary system is affecting on chemical peculiarities of those stars.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/156/47
- Title:
- DA white dwarfs from the Palomar Green Survey
- Short Name:
- J/ApJS/156/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Spectrophotometric observations at high signal-to-noise ratio were obtained of a complete sample of 347 DA white dwarfs from the Palomar Green (PG) Survey (1986, Cat. <II/207>). Fits of observed Balmer lines to synthetic spectra calculated from pure-hydrogen model atmospheres were used to obtain robust values of T_eff_, log(g), masses, radii, and cooling ages. The luminosity function of the sample, weighted by 1/V_max_, was obtained and compared with other determinations.
- ID:
- ivo://CDS.VizieR/J/ApJ/760/26
- Title:
- DA white dwarfs infrared photometry
- Short Name:
- J/ApJ/760/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present near- and mid-infrared photometry and spectroscopy from PAIRITEL, IRTF, and Spitzer of a metallicity-unbiased sample of 117 cool, hydrogen-atmosphere white dwarfs (WDs) from the Palomar-Green survey and find five with excess radiation in the infrared, translating to a 4.3^+2.7^_-1.2_% frequency of debris disks. This is slightly higher than, but consistent with the results of previous surveys. Using an initial-final mass relation, we apply this result to the progenitor stars of our sample and conclude that 1-7M_{sun}_ stars have at least a 4.3% chance of hosting planets; an indirect probe of the intermediate-mass regime eluding conventional exoplanetary detection methods. Alternatively, we interpret this result as a limit on accretion timescales as a fraction of WD cooling ages; WDs accrete debris from several generations of disks for ~10Myr. The average total mass accreted by these stars ranges from that of 200km asteroids to Ceres-sized objects, indicating that WDs accrete moons and dwarf planets as well as solar system asteroid analogs.
- ID:
- ivo://CDS.VizieR/J/A+A/363/1040
- Title:
- DB white dwarfs from the Hamburg/ESO survey
- Short Name:
- J/A+A/363/1040
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of 40 cool helium-rich white dwarfs found in the Hamburg/ESO survey. They were selected for follow-up spectroscopy because of their U-B colour below -0.18, the absence of strong absorption lines, and a continuum shape similar to that of a quasar. Effective temperatures for individual stars were determined by fitting model atmospheres of nearly pure helium with a small admixture of hydrogen. As a consequence of the selection criteria all but one sample stars have T_eff_ below 20000K. Four stars clearly show helium and hydrogen lines in their spectra. In the spectra of another three, helium, hydrogen, and metal lines can be detected. For these stars hydrogen and metal abundances were also determined by fitting appropriate model atmospheres containing these elements. Seven sample stars most likely have helium-rich atmospheres but do not show any helium lines. They either have featureless spectra or show calcium lines.
- ID:
- ivo://CDS.VizieR/J/ApJ/882/106
- Title:
- DB white dwarfs with SDSS and Gaia data
- Short Name:
- J/ApJ/882/106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive analysis of DB white dwarfs drawn from the Sloan Digital Sky Survey, based on model fits to ugriz photometry and medium-resolution spectroscopy from the Sloan Digital Sky Survey. We also take advantage of the exquisite trigonometric parallax measurements recently obtained by the Gaia mission. Using the so-called photometric and spectroscopic techniques, we measure the atmospheric and physical parameters of each object in our sample (Teff, logg, H/He, Ca/He, R, M), and compare the values obtained from both techniques in order to assess the precision and accuracy of each method. We then explore in great detail the surface gravity, stellar mass, and hydrogen abundance distributions of DB white dwarfs as a function of effective temperature. We present some clear evidence for a large population of unresolved double-degenerate binaries composed of DB+DB and even DB+DA white dwarfs. In the light of our results, we finally discuss the spectral evolution of DB white dwarfs, in particular the evolution of the DB-to-DA ratio as a function of Teff, and we revisit the question of the origin of hydrogen in DBA white dwarfs.
- ID:
- ivo://CDS.VizieR/J/ApJ/719/550
- Title:
- Deep NIR imaging of {rho} Oph cloud core
- Short Name:
- J/ApJ/719/550
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A search for young substellar objects in the {rho} Oph cloud core region has been made with the aid of multiband profile-fitting point-source photometry of the deep-integration Combined Calibration Scan images of the 2MASS extended mission in the J, H, and Ks bands, and Spitzer IRAC images at 3.6, 4.5, 5.8, and 8.0um. The field of view of the combined observations was 1{deg}x9.3', and the 5{sigma} limiting magnitude at J was 20.5. Comparison of the observed spectral energy distributions with the predictions of the COND and DUSTY models, for an assumed age of 1Myr, supports the identification of many of the sources with brown dwarfs and enables the estimation of effective temperature, T_eff_. The cluster members are then readily distinguishable from background stars by their locations on a plot of flux density versus T_eff_. The range of estimated T_eff_ values extends down to ~750K which, based on the COND model, would suggest the presence of objects of sub-Jupiter mass. The results also suggest that the mass function for the {rho} Oph cloud resembles that of the {sigma} Orionis cluster based on a recent study, with both rising steadily toward lower masses. The other main result from our study is the apparent presence of a progressive blueward skew in the distribution of J-H and H-Ks colors, such that the blue end of the range becomes increasingly bluer with increasing magnitude. We suggest that this behavior might be understood in terms of the "ejected stellar embryo" hypothesis, whereby some of the lowest-mass brown dwarfs could escape to locations close to the front edge of the cloud, and thereby be seen with less extinction.
- ID:
- ivo://CDS.VizieR/J/A+A/614/A46
- Title:
- delta Scuti stars <Teff>-{nu}max relation
- Short Name:
- J/A+A/614/A46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CoRoT and Kepler high-precision photometric data allowed the detection and characterization of the oscillation parameters in stars other than the Sun. Moreover, thanks to the scaling relations, it is possible to estimate masses and radii for thousands of solar-type oscillating stars. Recently, a {Delta}{nu}-{rho} relation has been found for delta Scuti stars. Now, analysing several hundreds of this kind of stars observed with CoRoT and Kepler, we present an empiric relation between their frequency at maximum power of their oscillation spectra and their effective temperature. Such a relation can be explained with the help of the {kappa}-mechanism and the observed dispersion of the residuals is compatible with they being caused by the gravity-darkening effect.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A59
- Title:
- delta Scuti stars with TESS
- Short Name:
- J/A+A/638/A59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Thanks to high-precision photometric data legacy from space telescopes like CoRoT and Kepler, the scientific community could detect and characterize the power spectra of hundreds of thousands of stars. Using the scaling relations, it is possible to estimate masses and radii for solar-type pulsators. However, these stars are not the only kind of stellar objects that follow these rules: delta Scuti stars seem to be characterized with seismic indexes such as the large separation. Thanks to long-duration high-cadence TESS light curves, we analysed more than two thousand of this kind of classical pulsators. In that way, we propose the frequency at maximum power as a proper seismic index since it is directly related with the intrinsic temperature, mass and radius of the star. This parameter seems not to be affected by rotation, inclination, extinction or resonances, with the exception of the evolution of the stellar parameters. Furthermore, we can constrain rotation and inclination using the departure of temperature produced by the gravity-darkening effect. This is especially feasible for fast rotators as most of delta Scuti stars seem to be.
- ID:
- ivo://CDS.VizieR/J/ApJ/681/1524
- Title:
- Detailed abundances for 28 metal-poor stars
- Short Name:
- J/ApJ/681/1524
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an abundance analysis for a sample of stars with -4<[Fe/H]<-2. The data were obtained with the HIRES spectrograph at Keck Observatory. The set includes 28 stars, with effective temperature ranging from 4800 to 6600K. For 13 stars with [Fe/H]<-2.6, including nine with [Fe/H]<-3.0 and one with [Fe/H]=-4.0, these are the first reported detailed abundances. For the most metal-poor star in our sample, CS 30336-049, we measure an abundance pattern that is very similar to stars in the range [Fe/H]~-3.5, including a normal C+N, abundance. We also find that it has very low but measurable Sr and Ba, indicating some neutron-capture activity even at this low of a metallicity. We explore this issue further by examining other very neutron capture-deficient stars and find that, at the lowest levels, [Ba/Sr] exhibits the ratio of the main r-process. We also report on a new r-process-enhanced star, CS 31078-018. This star has [Fe/H]=-2.85, [Eu/Fe]=1.23, and [Ba/Eu]=-0.51. CS 31078-018 exhibits an "actinide boost," i.e., much higher [Th/Eu] than expected and at a similar level to CS 31082-001. Our spectra allow us to further constrain the abundance scatter at low metallicities, which we then use to fit to the zero-metallicity Type II supernova yields of Heger & Woosley (2008arXiv0803.3161H). We find that supernovae with progenitor masses between 10 and 20M_{sun}_ provide the best matches to our abundances.
- ID:
- ivo://CDS.VizieR/J/ApJ/788/114
- Title:
- Detection of Kepler multiple M-star systems
- Short Name:
- J/ApJ/788/114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have searched the Kepler light curves of ~3900 M-star targets for evidence of periodicities that indicate, by means of the effects of starspots, rapid stellar rotation. Several analysis techniques, including Fourier transforms, inspection of folded light curves, "sonograms", and phase tracking of individual modulation cycles, were applied in order to distinguish the periodicities due to rapid rotation from those due to stellar pulsations, eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets with rotation periods, P_rot_<2 days, and 110 with P_rot_<1 day. Some 30 of the 178 systems exhibit two or more independent short periods within the same Kepler photometric aperture, while several have 3 or more short periods. Adaptive optics imaging and modeling of the Kepler pixel response function for a subset of our sample support the conclusion that the targets with multiple periods are highly likely to be relatively young physical binary, triple, and even quadruple M star systems. We explore in detail the one object with four incommensurate periods all less than 1.2 days, and show that two of the periods arise from one of a close pair of stars, while the other two arise from the second star, which itself is probably a visual binary. If most of these M-star systems with multiple periods turn out to be bound M-stars, this could prove a valuable way discovering young hierarchical M-star systems; the same approach may also be applicable to G and K stars. The ~5% occurrence rate of rapid rotation among the ~3900 M star targets is consistent with spin evolution models that include an initial contraction phase followed by magnetic braking, wherein a typical M star can spend several hundred Myr before spinning down to periods longer than 2 days.
