- ID:
- ivo://CDS.VizieR/J/A+A/379/162
- Title:
- Binaries with post-T Tauri secondaries
- Short Name:
- J/A+A/379/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- File table2 contains the values of the color indices: (b-y), m1, c1, H{beta}, from the Stroemgren photometry and the observational errors on these indices as given by the Hauck and Mermiliod (1998, Cat. <II/215>). The values of Teff and logg are obtained from the Moon & Dworetsky (1985MNRAS.217..305M) calibration to which we have implemented the corrections by Castelli (1991A&A...251..106C). The errors on the parameters Teff and logg, as explained in section 3.3, are the consequence of the observational error on the photometric indices; SigmaTeff is the total error, on Teff, computed as explained in section 3.3. File table5 contains the values of the parallax, the error on the parallax, the Teff and the luminosity for the early-type star and late type star of each visual binary system. The errors on the Teff and on the luminosity are taken into account to compute for each of these parameters its minimum and maximum value. File table7 gives the values of the ages and masses computed for the early-type stars from the Schaller et al. (1993, Cat. <J/A+AS/96/269>) isochrones and Meynet at al. (1993A&AS...98..477M) models and from the Girardi et al. (2000, Cat. <J/A+AS/141/371>) models. The errors on the Teff and the luminosity are used to compute the minimum and the maximum values for the age and the mass. The last two columns concern only the primary stars with a Teff greater than 15000K for which we also compute the age and the mass using as Teff value: (Teff-500K); 500K corresponds to the systematic shift between Teff derived by using different photometric system (see Sect. 3.3). File table9 gives the values of the ages and masses computed for the late-type components from the isochrones and evolutionary tracks by D'Antona et al. (1998, web page, http://www.mporzio.astro.it/~dantona/ ) Palla and Stahler (1999ApJ...525..772P), Siess et al. (2000A&A...358..593S) and Tout et al. (1999MNRAS.310..360T). When possible, the minimum and the maximum values of these parameters are given by taking into account the errors on the Teff and on the luminosity.
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- ID:
- ivo://CDS.VizieR/J/AJ/108/1722
- Title:
- Blue horizontal branch stars
- Short Name:
- J/AJ/108/1722
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A complete sample of blue horizontal branch (BHB) stars in the magnitude range 13.0<V<16.5 is isolated in two Galactic fields that have previously been searched for RR Lyrae variables: SA 57 in the Northern Polar Cap and the Lick Astrograph field RR 7 in the Anticenter (l=183{deg}, b=+37{deg}). These BHB stars are a subset of the AF stars found in the Case Low-Dispersion Northern Survey; lists of these AF stars were made available by the late Nick Sanduleak. The completeness of the sample was confirmed by reference to the photometric survey of SA 57 by Stobie & Ishida (1987AJ93..... 624S) that is complete to fainter than V=18. In the color range 0.00<(B-V)_0_<+0.20, we can distinguish the BHB stars among these AF stars by comparing them both with well known local field horizontal branch (FHB) stars and also the BHB members of the halo globular clusters M3 and M92. The criteria for this comparison include (1) a (u-B)_K_ color index (derived from photoelectric observations using the Stromgren u filter and the Johnson B and V filters) that measures the size of the Balmer jump, (2) a spectrophotometric index A that measures the steepness of the Balmer jump, and (3) a parameter D_0.2_ that is the mean width of the H{gamma} and H{delta} Balmer lines measured at 20 percent of the continuum level. These criteria give consistent results in separating BHB stars from higher gravity main sequence AF stars in the color range 0.00<(B-V)_0_<+0.20. All three photometric and spectrophotometric criteria were measured for 35 stars in the SA 57 field and 37 stars in the RR 7 field that are in the color range (B-V)_0_<+0.23 and in the magnitude range 13.0<V<16.5. For a small number of additional stars only (u-B)_K_ was obtained. Among the AF stars that are fainter than B=13 and bluer than (B-V)_0_=+0.23, about half of those in the SA 57 field and about one third of those in the lower latitude RR 7 field are BHB stars. Isoabundance contours were located empirically in plots of the pseudoequivalent width versus (B-V)_0_ for the lines of Mg II A4481{AA}, Ca II A3933 {AA} and Fe I A4272{AA}. Solar abundances were defined by the data from main sequence stars in the Pleiades and Coma open clusters. Data from the BHB stars in M3 and M92 defined the [Fe/H]=1.5 and -2.2 isoabundance contours, respectively. Metallicities of all stars were estimated by interpolating the measured pseudoequivalent widths in these diagrams at the observed (B-V)_0_. The distribution of [Fe/H] found for the BHB stars in this way is very similar to that which we found for the RR Lyrae stars in the same fields using the Preston AS method. The space densities of these BHB stars were analyzed both separately and together with earlier observations of field BHB stars given by Arnold & Gilmore (1992MNRAS.257..225A), Sommer-Larsen & Christensen (1986MNRAS.219..537S), and Preston et al. (1991ApJ...375..121P). This analysis supports a two-component model for the halo of our Galaxy that is similar in many respects to that proposed by Hartwick [The Galaxy (Reidel, Dordrecht 1987)] although our discussion refers only to the region outside the solar circle. For Z>=35kpc, a classical spherical halo dominates which follows a R_gal_^-3.5^ space-density law and which has a HB morphology like that of the globular cluster M3 (i.e., approximately equal numbers of BHB and RR Lyrae stars). Closer to the galactic plane, there is an additional component with a much flatter galactic distribution (scale height ~2.2kpc near the Sun). The stars of the two components do not have significantly different metallicity distributions but do have slightly different distributions of the A parameter which measures the steepness of the Balmer jump; this is the only physical criterion (independent of spatial or kinematic considerations) which distinguishes between the two components. If present estimates of the local RR Lyrae star space density are correct, then the ratio of BHB stars to RR Lyrae stars is higher in the flatter halo component. The flat component would then have a bluer HB morphology (which could be interpreted as making it older) than the spherical component. In the solar neighborhood about 80 percent of the BHB stars come from the flat component and about 20 percent from the spherical component. More than half of the AF stars with V>13.0 and (B-V)_0_<+0.23 are not BHB stars but have surface gravities that are more like those expected for main sequence stars. Their measured metallicities lie in the range -0.2<[Fe/H]<-2.3. The more metal-poor of these stars are probably similar to the blue metal-poor stars that have been discussed by Preston et al. (1994AJ....108..538P) which, while they probably include globular cluster blue stragglers as a subset, must also comprise stars of other types.
- ID:
- ivo://CDS.VizieR/J/A+A/557/A1
- Title:
- Bright B-type variables in Scorpius
- Short Name:
- J/A+A/557/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first two of a total of six nano-satellites that will constitute the BRITE-Constellation space photometry mission have recently been launched successfully. In preparation for this project, we carried out time-resolved colour photometry in a field that is an excellent candidate for BRITE measurements from space. We acquired 117h of Stromgren uvy data during 19 nights. Our targets comprised the {beta} Cephei stars {kappa} and {lambda} Sco, the eclipsing binary {mu}^1^ Sco, and the variable super/hypergiant {zeta}^1^ Sco. For {kappa} Sco, a photometric mode identification in combination with results from the spectroscopic literature suggests a dominant (l,m)=(1,-1) {beta} Cephei-type pulsation mode of the primary star. The longer period of the star may be a rotational variation or a g-mode pulsation. For {lambda} Sco, we recover the known dominant {beta} Cephei pulsation, a longer-period variation, and observed part of an eclipse. Lack of ultraviolet data precludes mode identification for this star. We noticed that the spectroscopic orbital ephemeris of the closer pair in this triple system is inconsistent with eclipse timings and propose a refined value for the orbital period of the closer pair of 5.95189+/-0.00003d. We also argue that the components of the {lambda} Sco system are some 30% more massive than previously thought. The binary light curve solution of {mu}^1^ Sco requires inclusion of the irradiation effect to explain the u light curve, and the system could show additional low amplitude variations on top of the orbital light changes. {zeta}^1^ Sco shows long-term variability on a time scale of at least two weeks that we prefer to interpret in terms of a variable wind or strange mode pulsations.
- ID:
- ivo://CDS.VizieR/J/ApJS/161/118
- Title:
- byH{alpha} photometry in open clusters
- Short Name:
- J/ApJS/161/118
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Be stars are a class of rapidly rotating B stars with circumstellar disks that cause Balmer and other line emission. There are three possible reasons for the rapid rotation of Be stars: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence (MS) evolution of B stars. To test the various formation scenarios, we have conducted a photometric survey of 55 open clusters in the southern sky. Of these, five clusters are probably not physically associated groups and our results for two other clusters are not reliable, but we identify 52 definite Be stars and an additional 129 Be candidates in the remaining clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/622/1052
- Title:
- byH{alpha} photometry of NGC 3766
- Short Name:
- J/ApJ/622/1052
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a technique to identify Be stars in open clusters using Stroemgren b, y, and narrowband H{alpha} photometry. We first identify the B-type stars of the cluster using a theoretical isochrone fit to the (b-y, y) color-magnitude diagram. The strongest Be stars are easily identified in a (b-y, y-H{alpha}) color-color diagram, but those with weaker H{alpha} emission (classified as possible Be star detections) may be confused with evolved or foreground stars. Here we present such photometry plus H{alpha} spectroscopy of members of the cluster NGC 3766 to demonstrate the accuracy of our technique.
- ID:
- ivo://CDS.VizieR/J/ApJS/219/7
- Title:
- Ca,by photometry in globular clusters. I. M22
- Short Name:
- J/ApJS/219/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the multiple stellar populations in one of the peculiar globular clusters (GCs), M22, using new ground-based wide-field Ca by and Hubble Space Telescope Wide-Field Camera 3 photometry with equivalent passbands, confirming our previous result that M22 has a distinctive red giant branch (RGB) split mainly due to the difference in metal abundances. We also make use of radial velocity measurements by others of the large number of cluster membership stars. Our main results are the following. (1) The RGB and the subgiant branch number ratios show that the calcium-weak (Ca-w) group is the dominant population of the cluster. However, an irreconcilable difference can be seen in the rather simple classification into two horizontal branches by others. (2) Each group has its own CN-CH anticorrelation. However, the alleged CN-CH positive correlation is likely illusory. (3) The location of the RGB bump of the calcium-strong (Ca-s) group is significantly fainter, which may pose a challenge to the helium enhancement scenario in the Ca-s group. (4) The positions of the centers are similar. (5) The Ca-w group is slightly more centrally concentrated, whereas the Ca-s is more elongated at larger radii. (6) The mean radial velocities for both groups are similar, but the Ca-s group has a larger velocity dispersion. (7) The Ca-s group rotates faster. The plausible scenario for the formation of M22 is that it formed via a merger of two GCs in a dwarf galaxy environment and accreted later to our Galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/109/2828
- Title:
- CaII H and K filter photometry II.
- Short Name:
- J/AJ/109/2828
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalog of 1990 stars on the Caby system is presented. The sample includes stars covering an extensive range in spectral type, luminosity class, and metallicity, as well as apparent magnitude. The hk indices are on the standard system defined in Anthony-Twarog et al. (1991AJ....101.1902A), while the V and (b-y) indices have been transformed to the system of Olsen (1993A&AS..102...89O), superseding the values in the original catalog of standard stars.
- ID:
- ivo://CDS.VizieR/J/AJ/116/1922
- Title:
- CaII H and K filter photometry III.
- Short Name:
- J/AJ/116/1922
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New photometry on the uvby Ca system is presented for over 300 stars. When combined with previous data, the sample is used to calibrate the metallicity dependence of the hk index for cooler, evolved stars. The metallicity scale is based upon the standardized merger of spectroscopic abundances from 38 studies since 1983, providing an overlap of 122 evolved stars with the photometric catalog. The hk index produces reliable abundances for stars in the [Fe/H] range from -0.8 to -3.4, losing sensitivity among cooler stars due to saturation effects at higher [Fe/H], as expected.
- ID:
- ivo://CDS.VizieR/J/A+A/498/527
- Title:
- Calibration of Stromgren phot. for late-type stars
- Short Name:
- J/A+A/498/527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The use of model atmospheres for deriving stellar fundamental parameters, such as Teff, log(g), and [Fe/H], will increase as we find and explore extreme stellar populations where empirical calibrations are not yet available. Moreover, calibrations for upcoming large satellite missions of new spectrophotometric indices, similar to the uvby-Hbeta system, will be needed. We aim to test the power of theoretical calibrations based on a new generation of MARCS models by comparisons with observational photometric data. We calculated synthetic uvby-Hbeta colour indices from synthetic spectra. A sample of 367 field stars, as well as stars in globular clusters, is used for a direct comparison of the synthetic indices versus empirical data and for scrutizing the possibilities of theoretical calibrations for temperature, metallicity, and gravity. We show that the temperature sensitivity of the synthetic (b-y) colour is very close to its empirical counterpart, whereas the temperature scale based upon Hbeta shows a slight offset. The theoretical metallicity sensitivity of the m1 index (and for G-type stars its combination with c1) is somewhat higher than the empirical one, based upon spectroscopic determinations. The gravity sensitivity of the synthetic c1 index shows satisfactory behaviour when compared to observations of F stars. For stars cooler than the sun, a deviation is significant in the c1-(b-y) diagram. The theoretical calibrations of (b-y), (v-y), and c1 seem to work well for Pop II stars and lead to effective temperatures for globular cluster stars supporting recent claims that atomic diffusion occurs in stars near the turnoff point of NGC 6397. Synthetic colours of stellar atmospheres can indeed be used, in many cases, to derive reliable fundamental stellar parameters. The deviations seen when compared to observational data could be due to incomplete linelists but are possibly also due to the effects of assuming plane-parallel or spherical geometry and LTE.
- ID:
- ivo://CDS.VizieR/J/AJ/129/1642
- Title:
- Calibration of synthetic photometry
- Short Name:
- J/AJ/129/1642
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new calibration of optical (UBV, Stroemgren uvby{beta}, and Geneva) and near-IR (Johnson RIJHK and Two Micron All Sky Survey) photometry for B and early A stars derived from Kurucz ATLAS9 model atmospheres. These models are then used to calibrate the synthetic photometry.
