- ID:
- ivo://CDS.VizieR/J/ApJ/786/120
- Title:
- Spectropolarimetric survey of classical Be stars
- Short Name:
- J/ApJ/786/120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent observational and theoretical studies of classical Be stars have established the utility of polarization color diagrams (PCDs) in helping to constrain the time-dependent mass decretion rates of these systems. We expand on our pilot observational study of this phenomenon, and report the detailed analysis of a long-term (1989-2004) spectropolarimetric survey of nine additional classical Be stars, including systems exhibiting evidence of partial disk-loss/disk-growth episodes as well as systems exhibiting long-term stable disks. After carefully characterizing and removing the interstellar polarization along the line of sight to each of these targets, we analyze their intrinsic polarization behavior. We find that many steady-state Be disks pause at the top of the PCD, as predicted by theory. We also observe sharp declines in the Balmer jump polarization for later spectral type, near edge-on steady-state disks, again as recently predicted by theory, likely caused when the base density of the disk is very high, and the outer region of the edge-on disk starts to self absorb a significant number of Balmer jump photons. The intrinsic V-band polarization and polarization position angle of {gamma} Cas exhibits variations that seem to phase with the orbital period of a known one-armed density structure in this disk, similar to the theoretical predictions of Halonen & Jones. We also observe stochastic jumps in the intrinsic polarization across the Balmer jump of several known Be+sdO systems, and speculate that the thermal inflation of part of the outer region of these disks could be responsible for producing this observational phenomenon. Finally, we estimate the base densities of this sample of stars to be between ~8x10^-11^ and ~4x10^-12^ g/cm^3^ during quasi steady state periods given there maximum observed polarization.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/875/29
- Title:
- Spectroscopic analysis of the CKS sample. I.
- Short Name:
- J/ApJ/875/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a quantitative spectroscopic analysis conducted on archival Keck/HIRES high-resolution spectra from the California-Kepler Survey (CKS) sample of transiting planetary host stars identified from the Kepler mission. The spectroscopic analysis was based on a carefully selected set of FeI and FeII lines, resulting in precise values for the stellar parameters of effective temperature (Teff) and surface gravity (logg). Combining the stellar parameters with Gaia DR2 parallaxes and precise distances, we derived both stellar and planetary radii for our sample, with a median internal uncertainty of 2.8% in the stellar radii and 3.7% in the planetary radii. An investigation into the distribution of planetary radii confirmed the bimodal nature of this distribution for the small-radius planets found in previous studies, with peaks at ~1.47+/-0.05 and ~2.72+/-0.10R_{Earth}_ with a gap at ~1.9R_{Earth}_. Previous studies that modeled planetary formation that is dominated by photoevaporation predicted this bimodal radii distribution and the presence of a radius gap, or photoevaporation valley. Our results are in overall agreement with these models, as well as core powered mass-loss models. The high internal precision achieved here in the derived planetary radii clearly reveal the presence of a slope in the photoevaporation valley for the CKS sample, indicating that the position of the radius gap decreases with orbital period; this decrease was fit by a power law of the form R_pl_{propto}P^-0.11^, which is consistent with both photoevaporation and core powered mass-loss models of planet formation, with Earth-like core compositions.
- ID:
- ivo://CDS.VizieR/J/ApJ/848/11
- Title:
- Spectroscopic and photometric analysis of WDs
- Short Name:
- J/ApJ/848/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed spectroscopic and photometric analysis of 219 DA and DB white dwarfs for which trigonometric parallax measurements are available. Our aim is to compare the physical parameters derived from the spectroscopic and photometric techniques, and then to test the theoretical mass-radius relation for white dwarfs using these results. The agreement between spectroscopic and photometric parameters is found to be excellent, especially for effective temperatures, showing that our model atmospheres and fitting procedures provide an accurate, internally consistent analysis. The values of surface gravity and solid angle obtained, respectively, from spectroscopy and photometry, are combined with parallax measurements in various ways to study the validity of the mass-radius relation from an empirical point of view. After a thorough examination of our results, we find that 73% and 92% of the white dwarfs are consistent within 1{sigma} and 2{sigma} confidence levels, respectively, with the predictions of the mass-radius relation, thus providing strong support to the theory of stellar degeneracy. Our analysis also allows us to identify 15 stars that are better interpreted in terms of unresolved double degenerate binaries. Atmospheric parameters for both components in these binary systems are obtained using a novel approach. We further identify a few white dwarfs that are possibly composed of an iron core rather than a carbon/oxygen core, since they are consistent with Fe-core evolutionary models.
- ID:
- ivo://CDS.VizieR/J/AJ/151/6
- Title:
- Spectroscopic and photometric properties of Tombaugh 1
- Short Name:
- J/AJ/151/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters can be the key to deepening our knowledge on various issues involving the structure and evolution of the Galactic disk and details of stellar evolution because a cluster's properties are applicable to all its members. However, the number of open clusters with detailed analysis from high-resolution spectroscopy or precision photometry imposes severe limitations on studies of these objects. To expand the number of open clusters with well-defined chemical abundances and fundamental parameters, we investigate the poorly studied, anticenter open cluster Tombaugh 1. Using precision uvbyCaH{beta} photometry and high-resolution spectroscopy, we derive the cluster's reddening, obtain photometric metallicity estimates, and, for the first time, present a detailed abundance analysis of 10 potential cluster stars (nine clump stars and one Cepheid). Using the radial position from the cluster center and multiple color indices, we have isolated a sample of unevolved, probable single-star members of Tombaugh 1. From 51 stars, the cluster reddening is found to be E(b-y)=0.221+/-0.006 or E(B-V)=0.303+/-0.008, where the errors refer to the internal standard errors of the mean. The weighted photometric metallicity from m_1_ and hk is [Fe/H]=-0.10+/-0.02, while a match to the Victoria-Regina Stromgren isochrones leads to an age of 0.95+/-0.10 Gyr and an apparent modulus of (m-M)=13.10+/-0.10. Radial velocities identify six giants as probable cluster members, and the elemental abundances of Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Y, Ba, Ce, and Nd have been derived for both the cluster and the field stars. Tombaugh 1 appears to be a typical inner thin disk, intermediate-age open cluster of slightly subsolar metallicity, located just beyond the solar circle, with solar elemental abundance ratios except for the heavy s-process elements, which are a factor of two above solar. Its metallicity is consistent with a steep metallicity gradient in the galactocentric region between 9.5 and 12 kpc. Our study also shows that Cepheid XZ CMa is not a member of Tombaugh 1 and reveals that this Cepheid presents signs of barium enrichment, making it a probable binary star.
- ID:
- ivo://CDS.VizieR/J/ApJ/821/8
- Title:
- Spectroscopic binary population of ONC and NGC2264
- Short Name:
- J/ApJ/821/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the spectroscopic binary population for two massive nearby regions of clustered star formation, the Orion Nebula Cluster (ONC) and NGC 2264, supplementing the data presented by Tobin et al. (2009, J/ApJ/697/1103) with more recent observations and more extensive analysis. The inferred multiplicity fraction up to 10 au based on these observations is 5.3+/-1.2% for NGC 2264 and 5.8+/-1.1% for the ONC; these values are consistent with the distribution of binaries in the field in the relevant parameter range. Eight of the multiple systems in the sample have enough epochs to perform an initial fit for the orbital parameters. Two of these sources are double-lined spectroscopic binaries; for them, we determine the mass ratio. Our reanalysis of the distribution of stellar radial velocities toward these clusters presents a significantly better agreement between stellar and gas kinematics than was previously thought.
- ID:
- ivo://CDS.VizieR/J/ApJ/868/57
- Title:
- Spectroscopic HR diagram of OB stars in the SMC
- Short Name:
- J/ApJ/868/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive stellar atmosphere analysis of 329 O- and B-type stars in the Small Magellanic Cloud (SMC) from the RIOTS4 survey. Using spectroscopically derived effective temperature Teff and surface gravities, we find that classical Be stars appear misplaced to low Teff and high luminosity in the spectroscopic Hertzsprung-Russell diagram (sHRD). Together with the most luminous stars in our sample, the stellar masses derived from the sHRD for these objects are systematically larger than those obtained from the conventional Hertzsprung-Russell diagram. This suggests that the well-known, spectroscopic mass-discrepancy problem may be linked to the fact that both groups of stars have outer envelopes that are nearly gravitationally unbound. The non-emission-line stars in our sample mainly appear on the main sequence, allowing a first estimate of the terminal-age main sequence (TAMS) in the SMC, which matches the predicted TAMS between 12 and 40M_{sun}_ at SMC metallicity. We further find a large underabundance of stars above ~25M_{sun}_ near the zero-age main sequence, reminiscent of such earlier findings in the Milky Way and Large Magellanic Cloud.
- ID:
- ivo://CDS.VizieR/J/AJ/152/207
- Title:
- Spectroscopic Indicators in SeisMic Archive (SISMA)
- Short Name:
- J/AJ/152/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We created a large database of physical parameters and variability indicators by fully reducing and analyzing the large number of spectra taken to complement the asteroseismic observations of the COnvection, ROtation and planetary Transits (CoRoT) satellite. 7103 spectra of 261 stars obtained with the ESO echelle spectrograph HARPS have been stored in the VO-compliant database Spectroscopic Indicators in a SeisMic Archive (SISMA), along with the CoRoT photometric data of the 72 CoRoT asteroseismic targets. The remaining stars belong to the same variable classes of the CoRoT targets and were observed to better characterize the properties of such classes. Several useful variability indicators (mean line profiles, indices of differential rotation, activity and emission lines) together with vsini and radial-velocity measurements have been extracted from the spectra. The atmospheric parameters T_eff_,logg, and [Fe/H] have been computed following a homogeneous procedure. As a result, we fully characterize a sample of new and known variable stars by computing several spectroscopic indicators, also providing some cases of simultaneous photometry and spectroscopy.
- ID:
- ivo://CDS.VizieR/J/A+A/649/A147
- Title:
- Spectroscopic parameters for 313 M dwarfs
- Short Name:
- J/A+A/649/A147
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The scientific community's interest on the stellar parameters of M dwarfs has been increasing over the last few years, with potential applications ranging from galactic characterization to exoplanet detection. The main motivation for this work is to develop an alternative and objective method to derive stellar parameters for M dwarfs using the H-band spectra provided by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Synthetic spectra generated with iSpec, Turbospectrum, MARCS models atmospheres and a custom made line list including over 1000000 water lines, are compared to APOGEE observations, and parameters are determined through {chi}^2^ minimization. Spectroscopic parameters (Teff, [M/H], logg, v_mic_) are presented for a sample of 313 M dwarfs, obtained from their APOGEE H-band spectra. The generated synthetic spectra reproduce observed spectra to a high accuracy level. The impact of the spectra normalization on the results are analyzed as well. Our output parameters are compared with the ones obtained with APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) for the same stellar spectrum, and we find that the values agree within the expected uncertainties. Comparisons with other previous near-infrared and optical literature are also available, with median differences within our estimated uncertainties found in most cases. Possible reasons for these differences are explored. The full H-band line list, the line selection for the synthesis, and the synthesized spectra are available for download, as are the calculated stellar parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/487/373
- Title:
- Spectroscopic parameters of 451 HARPS-GTO stars
- Short Name:
- J/A+A/487/373
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand the formation and evolution of solar-type stars in the solar neighborhood, we need to measure their stellar parameters to high accuracy. We present a catalogue of accurate stellar parameters for 451 stars that represent the HARPS Guaranteed Time Observations (GTO) "high precision" sample. Spectroscopic stellar parameters were measured using high signal-to-noise (S/N) spectra acquired with the HARPS spectrograph. The spectroscopic analysis was completed assuming LTE with a grid of Kurucz atmosphere models and the recent ARES code for measuring line equivalent widths. We show that our results agree well with those ones presented in the literature (for stars in common). We present a useful calibration for the effective temperature as a function of the index color B-V and [Fe/H]. We use our results to study the metallicity-planet correlation, namely for very low mass planets. The results presented here suggest that in contrast to their jovian counterparts, Neptune-like planets do not form preferentially around metal-rich stars. The ratio of Jupiter-to-Neptune is also an increasing function of stellar metallicity. These results are discussed in the context of the core-accretion model for planet formation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/397
- Title:
- Spectroscopic study of RGs in the Kepler field
- Short Name:
- J/MNRAS/450/397
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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 nine stars), we checked the accuracy of the determination method of stellar parameters previously applied to many red giants by Takeda et al. (2008PASJ...60..781T), since it may be possible to discriminate their complex evolutionary status by using the surface gravity versus 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 M_{sun}_) were found to be markedly larger by ~50 percent compared to the seismic values (~1-2 M_{sun}_) 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 versus effective temperature diagram. This consequence implies that the mass results of many red giants in the clump region determined by Takeda et al. 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.
