- ID:
- ivo://CDS.VizieR/J/MNRAS/466/546
- Title:
- Parameters for the 172 {lambda} Boo stars
- Short Name:
- J/MNRAS/466/546
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The evolutionary status of the chemically peculiar class of {lambda} Boo stars has been intensely debated. It is now agreed that the {lambda} Boo phenomenon affects A stars of all ages, from star formation to the terminal age main sequence, but the cause of the chemical peculiarity is still a puzzle. We revisit the debate of their ages and temperatures in order to shed light on the phenomenon, using the new parallaxes in Gaia Data Release 1 with existing Hipparcos parallaxes and multicolour photometry. We find that no single formation mechanism is able to explain all the observations, and suggest that there are multiple channels producing {lambda} Boo spectra. The relative importance of these channels varies with age, temperature and environment.
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- ID:
- ivo://CDS.VizieR/J/A+A/581/A138
- Title:
- Photometric variability in magnetic CP stars
- Short Name:
- J/A+A/581/A138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The (magnetic) chemically peculiar (CP) stars of the upper main sequence are well-suited laboratories for investigating the influence of magnetic fields on the stellar surface because they produce abundance inhomogeneities (spots), which results in photometric variability that is explained in terms of the oblique rotator model. CP stars exhibiting this phenomenon are normally classified as {alpha}^2^ Canum Venaticorum (ACV) variables. It is important to increase the sample of known rotational periods among CP stars by discovering new ACV variables. An increased sample size will contribute to the understanding of the CP stars' evolution in time. We aim at discovering new ACV variables in the public data of the third phase of the All Sky Automated Survey (ASAS-3). Furthermore, by analysis of the available photometric data, we intend to derive rotational periods of the stars. The ASAS-3 data were cross-correlated with the Catalogue of Ap, HgMn, and Am stars in order to analyse the light curves of bona fide CP and related stars. The light curves were downloaded and cleaned of outliers and data points with a flag indicating bad quality. Promising candidates showing a larger scatter than observed for constant stars in the corresponding magnitude range were searched for periodic signals using a standard Fourier technique. Objects exhibiting periodic signals well above the noise level were considered and visually inspected, whereas borderline cases were rejected. In total, we found 323 variables, from which 246 are reported here for the first time, and 77 were probably wrongly classified before. The observed variability pattern of most stars is in accordance with an ACV classification. For some cases, it is difficult to distinguish between the light curves of double-waved ACVs and the variability induced by orbital motion (ellipsoidal variables/eclipsing variables), especially for objects exhibiting very small amplitudes and/or significant scatter in their light curves. Thus, some eclipsing or rotating ellipsoidal variables might be present. However, we are confident that the given periods are the correct ones. There seems to be a possible weak correlation between the rotational period and colour, in the sense that cooler magnetic CP stars rotate more slowly. However, this correlation seems to disappear when correcting for the interstellar reddening. The next steps have to include a compilation of all available rotational periods from the literature and a detailed investigation of the astrophysical parameters of these stars. This includes a determination of the individual masses, luminosities, ages, and inclination angles. However, this information cannot be straightforwardly determined from photometric data alone.
- ID:
- ivo://CDS.VizieR/J/A+AS/128/245
- Title:
- Photometry of chemically peculiar stars
- Short Name:
- J/A+AS/128/245
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Differential Stroemgren uvby photometric observations from the Four College Automated Photoelectric Telescope are presented for four Chemically Peculiar stars of the upper main sequence: the HgMn star binary AR Aurigae and the magnetic stars 3 Hydrae, 49 Cancri, and BX Bootis. AR Aurigae shows little variability except during the primary and secondary eclipses. The 11.305 day period of Maitzen et al. for 3 Hya is confirmed. A new period of 7.0501 days is found for 49 Cancri while a slightly refined period of 2.88756 days is derived for BX Boo.
- ID:
- ivo://CDS.VizieR/J/PASP/109/9
- Title:
- Photometry of chemically peculiar stars
- Short Name:
- J/PASP/109/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Differential Stromgren uvby photometric observations from the Four College Automated Photoelectric Telescope of four magnetic Chemically Peculiar stars are used to refine rotational periods and to define the shapes of the light curves. HR 1643 (P=2.73475d) shows large phase variability in all four magnitudes. Theta Aur (P=3.6188d) exhibits large amplitude variations with two components contributing to the minima. For 49 Cam (P=4.28679d), we probably are observing both polar regions and much of the surface. The values for HR 3724 (P=33.984d) confirm Wolff's result that the main variability is in v.
- ID:
- ivo://CDS.VizieR/J/A+AS/111/41
- Title:
- Photometry of magnetic CP stars
- Short Name:
- J/A+AS/111/41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photometry in the Stroemgren and Geneva systems is used to improve the ephemerides of the magnetic CP stars 56 Tau, HD 111133, HD 126515 and HD 215441.
- ID:
- ivo://CDS.VizieR/J/MNRAS/453/3766
- Title:
- Project VeSElkA: HD stars atomic-line analysis
- Short Name:
- J/MNRAS/453/3766
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A portion of main-sequence stars, called chemically peculiar (CP) stars, show important abundance anomalies mainly due to atomic diffusion of the species within these stars. Certain CP stars have hydrodynamically stable atmospheres where atomic diffusion may dominate and lead to vertical abundance stratification there. Recently, Project VeSElkA (a word meaning rainbow in Ukrainian and standing for "Vertical Stratification of Element Abundances") was initiated with the goal to detect vertical stratification of chemical abundances in selected CP stars using high-resolution spectra with large signal-to-noise ratios. The first extensive and detailed series of results from atomic-line analysis is presented here for four stars of Project VeSElkA: HD 71030, HD 95608, HD 116235 and HD 186568. These stars were recently observed with ESPaDOnS at Canada-France-Hawaii Telescope. Strong evidence of iron stratification in the atmospheres of HD 95608 and HD 116235 was found. Chromium also shows a steep abundance gradient in the upper atmospheres of these two stars. No evidence of stratification is found for HD 71030 and HD 186568.
- ID:
- ivo://CDS.VizieR/J/A+A/324/949
- Title:
- Properties of He-rich stars I.
- Short Name:
- J/A+A/324/949
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A determination of the surface gravity and an abundance analysis of helium in a sample of 17 He-rich and 5 normal, reference stars is presented. These results are derived from low resolution CCD spectra, but each star was measured at least 6 times in order to obtain a significant average spectrum for the spectroscopic variables. The helium abundances derived from the models used are very close to 0.1 for normal, reference stars and are larger for the others, clearly indicating the He-rich phenomenon in them. NLTE effects, errors on the microturbulence value or on the surface gravity do not influence the estimated helium abundances. Nevertheless, synthesized Geneva colours are affected by the He-rich peculiarity, especially the [U-B] index which systematically changes by -0.025 mag per 0.1 of He abundance for the coolest stars in the sample. We cannot confirm the correlation between the evolutionary state and the helium abundance reported previously (Zboril et al. 1994, in "International Conference on CP and Magnetic Stars.", Tatranska Lomnica, eds. J. Zverko and J. Ziznovsky, p. 105), although we used a more reliable technique of log(g) determination. All He-rich objects lie within the main sequence: their surface gravities are all inside the range 4.1<logg<4.5, with no more than three objects having logg<4.25. We find a significant spread of helium abundances in this range of surface gravities, from the solar value ~0.1 up to about 0.4. Some of the programme stars (including reference stars) present emission in their Balmer lines and therefore some kind of stellar activity. Strong helium overabundance often coexists with emission and stellar activity.
- ID:
- ivo://CDS.VizieR/J/A+A/363/1051
- Title:
- Properties of He-rich stars. III.
- Short Name:
- J/A+A/363/1051
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of helium rich atmospheres in the interval He/H 0.1-1.0 as derived from fully consistent model computations for effective temperature (from 15000K up to 32000K) and surface gravity (log(g)=3.5 and 4.0).
- ID:
- ivo://CDS.VizieR/J/A+A/621/A108
- Title:
- Radial velocity compilation for 45 CEMP-no stars
- Short Name:
- J/A+A/621/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Carbon-enhanced metal-poor (CEMP) stars comprise a high percentage of stars at the lowest metallicities. The stars in the CEMP-no subcategory do not show any s-process enhancement and therefore cannot easily be explained by transfer of carbon and s-process elements from a binary AGB companion. We have performed radial velocity monitoring of a sample of 22 CEMP-no stars to further study the role that binarity plays in this type of CEMP star. We find four new binary CEMP-no stars based on their radial velocity variations; this significantly enlarges the population of known binaries to a total of 11. One of the new stars found to be in a binary system is HE 0107-5240, which is one of the most iron-poor stars known. This supports the binary transfer model for the origin of the abundance pattern of this star.We find a difference in binary fraction in our sample that depends on the absolute carbon abundance, with a binary fraction of 47 (+15/-14) % for stars with a higher absolute carbon abundance and 18 (+14/-9) % for stars with a lower absolute carbon abundance. This might imply a relation between a high carbon abundance and the binarity of a metal-poor star. Although binarity does not equate to mass transfer, there is a possibility that a CEMP-no star in a binary system has been polluted, and care has to be taken in the interpretation of their abundance patterns. We furthermore demonstrate the potential of Gaia of discovering additional binary candidates.
- ID:
- ivo://CDS.VizieR/J/A+A/457/1033
- Title:
- Radial velocity of HR 7224
- Short Name:
- J/A+A/457/1033
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HR 7224 is a rapidly rotating He-weak silicon star known as photometrically variable with a period of 1.123d. Drastic changes of photometric amplitude and period were reported in 2003. We investigate the star spectroscopically to determine the time scales of variability, to derive basic atmospheric parameters, and to give first estimates on possible surface structures. We investigate time series of more then 570 high-resolution spectra of HR 7224 for radial velocity and line profile variations. The rotation period is determined from period analysis of data. Comparing radial velocity and line profile variations we draw first conclusions on possible surface structures in terms of line strengths. From Balmer and metal lines we determine Teff, log(g), vsini and metal abundances depending on rotation phase. The star shows a remarkable half-amplitude of radial velocity variation of 6km/s. From this variation we deduce a rotation period of 1.12324d. The period and the double-wave shaped radial velocity curve are in agreement with earlier photometric findings. The observed radial velocity variations can be explained by the rotation period and its harmonics and no further periodic contributions were found in the residuals. HR 7224 has enhanced Si and Fe abundances whereas He is extremely depleted. The star shows line strength variations of all observed elements with the rotation period. Variations of radial velocity, line strength and line shape of silicon lines and their relationships can be explained by assuming two large spots on the stellar surface showing enhanced line strength. From Balmer lines we deduce different temperatures of the star for different rotation phases. The observed difference in amplitudes of the variation of Mg II and Si II lines supports the assumption of surface regions of different temperature on this presumably magnetic CP star. Synthetic uvby colors computed from adapted synthetic spectra confirm the high photometric amplitude reported for the 2003 light curves.
