- ID:
- ivo://CDS.VizieR/II/43
- Title:
- K-line photometry of Southern A stars
- Short Name:
- II/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The photoelectric measurements of the strength of the Calcium K-line has been extended by 223 stars of predominantly southern or equatorial declinations which are well distributed in right ascension. This has expanded the existent list to 369 field stars for which a k-index is available, including many more Am stars. All available k-index data for field stars are presented here.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/24/35
- Title:
- LMC A-F supergiants
- Short Name:
- J/A+AS/24/35
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A survey for A-F type supergiants in the Large Magellanic Cloud has been carried out using UV objective prism plates. 890 objects were detected and their spectral types, luminosity classes, magnitudes, and precise positions determined. The survey is practically complete to m_pg_=12.5 and extends for certain types of stars to m_pg_=14. It is found that the spatial distribution of the A-F supergiants is not correlated with the distribution of the gas and OB stars of the cloud. This is evidence in support of the tentative identification by Stock and Wroblewski of early-type galactic supergiants well off the plane. Several other implications of this result are also discussed.
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/2765
- Title:
- Orbital motion monitoring of A-star multiples
- Short Name:
- J/MNRAS/422/2765
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As a part of our ongoing Volume-limited A-Star (VAST) adaptive optics survey, we have obtained observations of 26 binary systems with projected separations <100AU, 13 of which have sufficient historical measurements to allow for refinement of their orbital elements. For each system with an estimated orbit, the dynamical system mass obtained was compared with the system mass estimated from mass-magnitude relations. Discrepancies between the dynamical and theoretical system mass can be explained by the presence of a previously unresolved spectroscopic component, or by a non-solar metallicity of the system. Using this approach to infer the presence of additional companions, a lower limit to the fraction of binaries, triples, and quadruples can be estimated as 39%, 46%, and 15%, for systems with at least one companion within 100AU. The fraction of multiple systems with three or more components shows a relative increase compared to the fraction for Solar-type primaries resolved in previous volume-limited surveys. The observations have also revealed a pair of potentially young (<100Myr) M-dwarf companions, which would make an ideal benchmark for the theoretical models during the pre-Main Sequence contraction phase for M-dwarfs. In addition to those systems with orbit fits, we report 13 systems for which further orbital monitoring observations, are required, 11 of which are newly resolved as a part of the VAST survey.
- ID:
- ivo://CDS.VizieR/J/A+A/554/A108
- Title:
- Periodic variables in NGC 3766
- Short Name:
- J/A+A/554/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the population of periodic variable stars in the open cluster NGC3766 based on a 7-year multiband monitoring campaign conducted on the 1.2m Swiss Euler telescope at La Silla, Chili. The data reduction, light curve cleaning, and period search procedures, combined with the long observation time line, allowed us to detect variability amplitudes down to the mmag level. The variability properties were complemented with the positions in the color-magnitude and color-color diagrams to classify periodic variable stars into distinct variability types. We find a large population (36 stars) of new variable stars between the red edge of slowly pulsating B (SPB) stars and the blue edge of delta Sct stars, a region in the Hertzsprung-Russell (HR) diagram where no pulsation is predicted to occur based on standard stellar models. The bulk of their periods ranges from 0.1 to 0.7d, with amplitudes between 1 and 4mmag for the majority of them. About 20% of stars in that region of the HR diagram are found to be variable, but the number of members of this new group is expected to be higher, with amplitudes below our mmag detection limit. The properties of this new group of variable stars are summarized and arguments set forth in favor of a pulsation origin of the variability, with g-modes sustained by stellar rotation. Potential members of this new class of low-amplitude periodic (most probably pulsating) A and late-B variables in the literature are discussed. We additionally identify 16 eclipsing binary, 13 SPB, 14 delta Sct, and 12 gamma Dor candidates, as well as 72 fainter periodic variables. All are new discoveries. We encourage searching for this new class of variables in other young open clusters, especially in those hosting a rich population of Be stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/441/3543
- Title:
- Possible planets around A stars
- Short Name:
- J/MNRAS/441/3543
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kepler photometry of A stars shows that a considerable fraction (about 19 per cent) have a peculiar feature in the periodogram. This feature consists of a broad peak, thought to be due to differential rotation in a spotted star, and a sharp peak at slightly higher frequency. The pattern clearly involves some widespread stellar property and the sharp peak implies a strictly coherent periodicity. We investigate the possibility that the periodicity is due to rotation, pulsation or an orbital effect. We argue that neither rotation nor pulsation can provide a suitable, testable, explanation. We suggest that the sharp feature could be due to a planet in synchronous orbit around the rapidly rotating, spotted A star, not necessarily in transit. Spectroscopic observations of sufficient precision are required to falsify this hypothesis.
- ID:
- ivo://CDS.VizieR/J/AJ/121/2148
- Title:
- Precise spectral types for 372 A, F & G stars
- Short Name:
- J/AJ/121/2148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first in a series of two papers that address the problem of the physical nature of luminosity classification in the late A-, F-, and early G-type stars. In this paper, we present precise spectral classifications of 372 stars on the MK system. For those stars in the set with Stroemgren uvby{beta} photometry, we derive reddenings and present a calibration of MK temperature types in terms of the intrinsic Stroemgren (b-y)_0_ index. We also examine the relationship between the luminosity class and the Stroemgren c_1_ index, which measures the Balmer jump. The second paper will address the derivation of the physical parameters of these stars, and the relationships between these physical parameters and the luminosity class. Stars classified in this paper include one new {lambda} Bootis star and 10 of the F- and G-type dwarfs with recently discovered planets.
- ID:
- ivo://CDS.VizieR/III/134
- Title:
- Radial Velocities of Bright Population II F Stars
- Short Name:
- III/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog presents new radial velocity determinations, based on 2nm/mm Coude plates, for 146 southern stars brighter than m(v)=8.3. Drawn from the catalog of uvby-{beta} photometry of southern A5-G0 stars by Olsen (1983, Cat. II/90), the program stars are certain or suspected Population II stars. One triple-lined and 10 double-lined binaries have been detected, including HD 210737, for which a preliminary orbit has been derived. Notes on spectral peculiarities are given. The catalog is in two files. The first file lists HD number, heliocentric Julian date of observation, radial velocity with error and number of lines observed for both the primary and secondary stars, rotation class, and remarks for each observation. The second file contains additional remarks to the data of the first file, sorted by HD number.
- ID:
- ivo://CDS.VizieR/J/A+A/381/105
- Title:
- Rotational velocities of A-type stars. I.
- Short Name:
- J/A+A/381/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Within the scope of a Key Programme determining fundamental parameters of stars observed by HIPPARCOS, spectra of 525 B8 to F2-type stars brighter than V=8 have been collected at ESO. Fourier transforms of several line profiles in the range 4200-4500{AA} are used to derive vsini from the frequency of the first zero. Statistical analysis of the sample indicates that measurement error is a function of vsini and this relative error of the rotational velocity is found to be about 6% on average. The results obtained are compared with data from the literature. There is a systematic shift from standard values from Slk_7_5, which are 10 to 12% lower than our findings. Comparisons with other independent vsini values tend to prove that those from Slettebak et al. (1975ApJS...29..137S) are underestimated. This effect is attributed to the presence of binaries in the standard sample of Slettebak et al. (1975ApJS...29..137S), and to the model atmosphere they used.
- ID:
- ivo://CDS.VizieR/J/A+A/463/671
- Title:
- Rotational velocities of A-type stars. III.
- Short Name:
- J/A+A/463/671
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of vsini of B9 to F2-type main sequence single stars has been built from highly homogeneous vsini parameters determined for a large sample cleansed of objects presenting the Am and Ap phenomenon as well as of all known binaries. The aim is to study the distributions of rotational velocities in the mass range of A-type stars for normal single objects. Robust statistical methods are used to rectify the vsini distributions for the projection effect and the error distribution. The equatorial velocity distributions are obtained for about 1100 stars divided in six groups defined by the spectral type, under the assumption of randomly orientated rotational axes. We show that late B and early A-type main-sequence stars have genuine bimodal distributions of true equatorial rotational velocities probably due to angular momentum loss and redistribution that the star underwent before reaching the main sequence. A striking lack of slow rotators is noticed among intermediate and late A-type stars.
- ID:
- ivo://CDS.VizieR/J/A+A/537/A120
- Title:
- Rotational velocities of A-type stars. IV.
- Short Name:
- J/A+A/537/A120
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In previous works of this series, we have shown that late B- and early A-type stars have genuine bimodal distributions of rotational velocities and that late A-type stars lack slow rotators. The distributions of the surface angular velocity ratio Omega/Omega_crit_ (Omega_crit_ is the critical angular velocity) have peculiar shapes according to spectral type groups, which can be caused by evolutionary properties. We aim to review the properties of these rotational velocity distributions in some detail as a function of stellar mass and age. We have gathered vsini for a sample of 2014 B6- to F2-type stars. We have determined the masses and ages for these objects with stellar evolution models. The (Teff,logL/L_{sun}_)-parameters were determined from the uvby-beta photometry and the HIPPARCOS parallaxes.
