- ID:
- ivo://CDS.VizieR/J/MNRAS/449/1401
- Title:
- Am stars candidates from LAMOST DR1
- Short Name:
- J/MNRAS/449/1401
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of metallic-line star (Am) candidates from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) Data Release One (DR1). According to the characteristic of underabundance of calcium and overabundance of iron element of Am stars, we propose an empirical separation curve derived from line indices of Ca ii K line and iron lines we choose for low-resolution spectra. Ultimately, 3537 Am candidates are selected from more than 30000 stars, which are classified as A-type or early F-type stars by both the LAMOST pipeline and visual inspection. Then, we carry out some analysis on this sample and finally provide a list of the Am candidates with 10 relevant parameters. Compared with other catalogues, Am candidates selected from the LAMOST DR1 are much fainter on the whole. Obviously, our list is an important complement to already known bright Am catalogues, and it offers valuable material for research on this type of chemically peculiar star.
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- ID:
- ivo://CDS.VizieR/J/AJ/129/2026
- Title:
- Differential photometry of HD 8801
- Short Name:
- J/AJ/129/2026
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have discovered the first example of a star pulsating intrinsically with both {gamma} Doradus and {delta} Scuti frequencies. HD 8801 is an Am metallic-line star that appears to be single. Since the vast majority of Am stars are members of binary systems with periods less than 1000 days and also do not pulsate, HD 8801 possesses a very unusual, if not unique, combination of physical properties. Our photometry, acquired with an automatic telescope at Fairborn Observatory, resolves six independent pulsation periods between 0.048 and 0.404 days. The two longest periods lie within the range of {gamma} Dor variables, while the four shorter periods are within the range of {delta} Sct stars.
- ID:
- ivo://CDS.VizieR/III/162A
- Title:
- General Catalogue of Ap and Am stars
- Short Name:
- III/162A
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalogue of all Ap and Am stars ever discovered is presented. It contains 6684 objects, including those which have been wrongly considered as Ap or Am stars, and those which are probable Ap or Am stars.
- ID:
- ivo://CDS.VizieR/III/260
- Title:
- General Catalogue of Ap and Am stars
- Short Name:
- III/260
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalogue of 8205 known or suspected Ap, HgMn and Am stars is presented. This is a major update of the catalogue of Ap and Am stars (Renson et al., 1991, III/162). It includes revised identifications, additional stars and revised information. Bertaud and GC identifications were suppressed. HIP and TYC identifications were added. The GC number can be found in notes N for stars without HIP number and for double stars when the components have different numbers (the GC of the other component is then given in note D).
- ID:
- ivo://CDS.VizieR/J/AJ/162/32
- Title:
- LAMOST parameters of Am and non-chemical-peculiar stars
- Short Name:
- J/AJ/162/32
- Date:
- 21 Mar 2022 00:10:05
- Publisher:
- CDS
- Description:
- Rotation is a critical physical process operating in the formation of Am stars. There is a strong correlation between low-velocity rotation and chemical peculiarity. However, the existence of many non-chemical-peculiar slow rotators challenges the understanding of Am stars. The purpose of our work is to search for low-velocity rotating non-chemical-peculiar A-type stars and Am stars and to make a comparative analysis. In this paper, we pick out a sample from the LAMOST-Kepler project, including 21 Am stars, 125 non-chemical-peculiar slow rotators, and 53 non-chemical-peculiar fast rotators. We calculate the rotational frequencies through a periodic change of light curves caused by inhomogeneous stellar surfaces and then obtain the rotational velocities. For slow rotators, the age of Am stars is statistically younger than that of non-chemical-peculiar stars in the same temperature bin. In the comparison of the period, the average amplitude, and stellar mass of Am and non-chemical-peculiar stars, we discover that there is no difference in the photometric variability between Am and non-chemical-peculiar stars, which implies similar inhomogeneities on the surfaces. The average amplitude of non-chemical-peculiar stars has a downward trend with the increase of effective temperature and stellar mass, which is consistent with the theoretical prediction caused by weak dynamo-generated magnetic fields in A-type stars. In addition, we confirm four non-chemical-peculiar stars that have flares by checking field-of-view images, pixel images, and pixel-level light curves.
- ID:
- ivo://CDS.VizieR/J/AJ/153/218
- Title:
- New IR photometric study of Ap and Am stars
- Short Name:
- J/AJ/153/218
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, 426 well known confirmed Ap and Am stars are photometrically studied in the infrared. The 2MASS, Wide-field Infrared Survey Explorer (WISE), and IRAS data are employed to make analyses. The results in this paper have shown that in the 1-3 {mu}m region over 90% Ap and Am stars have no or little infrared excesses, and infrared radiations in the near-infrared from these stars are probably dominated by the free-free emissions. It is also shown that in the 3-12 {mu}m region, the majority of Ap stars and Am stars have very similar behavior, i.e., in the W1-W2 (3.4-4.6 {mu}m) region, over half of Ap and Am stars have clear infrared excesses, which are possibly due to the binarity, the multiplicity, and/or the debris disk, but in the W2-W3 (4.6-12 {mu}m) region they have no or little infrared excess. In addition, in the 12-22 {mu}m region, some of Ap stars and Am stars show the infrared excesses and infrared radiations for these Ap and Am stars are probably due to the free-free emissions. In addition, it is seen that the probability of being the binarity, the multiplicity and/or the debris disk for Am stars is much higher than that for Ap stars. Furthermore, it can be seen that, in general, no relations can be found between infrared colors and spectral types either for Ap stars or for Am stars.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A83
- Title:
- PCA-based inversion of stellar parameters
- Short Name:
- J/A+A/589/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an automated procedure that simultaneously derives the effective temperature Teff, surface gravity logg, metallicity [Fe/H], and equatorial projected rotational velocity vsini for "normal" A and Am stars. The procedure is based on the principal component analysis (PCA) inversion method, which we published in a recent paper. A sample of 322 high-resolution spectra of F0-B9 stars, retrieved from the Polarbase, SOPHIE, and ELODIE databases, were used to test this technique with real data. We selected the spectral region from 4400-5000 Ang as it contains many metallic lines and the Balmer H{beta} line. Using three data sets at resolving powers of R=42000, 65000 and 76000, about ~6.6x10^6 synthetic spectra were calculated to build a large learning database. The Online Power Iteration algorithm was applied to these learning data sets to estimate the principal components (PC). The projection of spectra onto the few PCs offered an efficient comparison metric in a low-dimensional space. The spectra of the well-known A0- and A1-type stars, Vega and Sirius A, were used as control spectra in the three databases. Spectra of other well-known A-type stars were also employed to characterize the accuracy of the inversion technique. We inverted all of the observational spectra and derived the atmospheric parameters. After removal of a few outliers, the PCA-inversion method appeared to be very efficient in determining Teff, [Fe/H], and vsini for A/Am stars. The derived parameters agree very well with previous determinations. Using a statistical approach, deviations of around 150K, 0.35dex, 0.15dex, and 2km/s were found for Teff, logg, [Fe/H], and vsini with respect to literature values for A-type stars. The PCA inversion proves to be a very fast, practical, and reliable tool for estimating stellar parameters of FGK and A stars and for deriving effective temperatures of M stars.
- ID:
- ivo://CDS.VizieR/J/A+A/470/1009
- Title:
- Radial velocities of HD 209625
- Short Name:
- J/A+A/470/1009
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The goal is to test the structure of hot metallic stars, and in particular the structure of a near-surface convection zone using asteroseismic measurements. Indeed, stellar models including a detailed treatment of the radiative diffusion predict the existence of a near-surface convection zone in order to correctly reproduce the anomalies in surface abundances that are observed in Am stars. The Am star HD 209625 was observed with the Harps spectrograph mounted on the 3.6-m telescope at the ESO La Silla Observatory (Chile) during 9 nights in August 2005. This observing run allowed to collect 1243 radial velocity measurements, with a standard deviation of 1.35m/s. The power spectrum associated with these RV measurements does not present any excess. Therefore, either the structure of the external layers of this star does not enable to excite solar-like oscillations, or the amplitudes of the oscillations remains below 20-30cm/s (depending of their frequency range).
- ID:
- ivo://CDS.VizieR/J/A+A/354/881
- Title:
- Radial velocities of Praesepe & Hyades Am stars
- Short Name:
- J/A+A/354/881
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CORAVEL radial-velocity observations of Am stars in the Hyades and Praesepe have allowed the determination of orbital elements for 10 spectroscopic binaries, among which 3 are first determinations. One Am star (KW 40) is found to be a well hierarchised triple system. KW 538 has a rather long period (435 days) for an Am star. Orbits of systems with periods shorter than 8.5 days are circularized, or present eccentricities smaller than 0.04. For 19 Am stars, the number of quadruple-, triple-, double-, single systems is 1:2:14(10+4?):(2?). The Am stars in a ({beta}, B-V) diagram clearly stand away by 0.03mag from the sequence defined by normal main-sequence stars. This diagram could be a powerful method to identify Am stars in more distant open clusters, provided there is no differential reddening. In the colour-magnitude diagram (M_V_, {beta}), double-lined binaries are 0.6-0.7mag above the ZAMS as expected, while most single-lined are close to or on the ZAMS because the secondary does not contribute much light. The absence of X-ray detection of 4 systems in the Hyades is an argument for the presence of a white dwarf secondary.
- ID:
- ivo://CDS.VizieR/J/AJ/159/43
- Title:
- Spectroscopically identified CVs from LAMOST survey. I.
- Short Name:
- J/AJ/159/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of cataclysmic variables (CVs) is presented including spectroscopically identified 380 spectra of 245 objects, of which 58 CV candidates are new discoveries. The BaggingTopPush and the Random Forest algorithms are applied to the Fifth Data Release (DR5) of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to retrieve CVs with strong emission lines and with broad absorption lines respectively. Based on spectroscopic classification, 134 dwarf novae, 41 nova-like variables, and 19 magnetic CVs are identified from the sample. In addition, 89 high-inclination systems and 33 CVs showing companion stars are recognized and discussed for their distinct spectral characteristics. Comparisons between CVs from LAMOST and from published catalogs are made in spatial and magnitude distribution, and the difference of their locus in the Gaia color-absolute magnitude diagram (CaMD) are also investigated. More interestingly, for two dwarf novae observed through LAMOST and SDSS in different epochs, their spectra both in quiescence phase and during outburst are exhibited.
