- ID:
- ivo://CDS.VizieR/J/A+A/373/625
- Title:
- uvby{beta} photometry of lambda Bootis stars
- Short Name:
- J/A+A/373/625
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Lambda Bootis stars comprise only a small number of all A-type stars and are characterized as nonmagnetic, Population I, late B to early F-type dwarfs which show significant underabundances of metals whereas the light elements (C, N, O and S) are almost normal abundant compared to the Sun. In the second paper on a spectroscopic survey for lambda Bootis stars, we present the spectral classifications of all program stars observed. These stars were selected on the basis of their Stromgren uvbybeta colors as lambda Bootis candidates. In total, 708 objects in six open clusters, the Orion OB1 association and the Galactic field were classified. In addition, nine serendipity non-candidates in the vicinity of our program stars as well as 15 Guide Star Catalogue stars were observed resulting in a total of 732 classified stars. The 15 objects from the Guide Star Catalogue are part of a program for the classification of apparent variable stars from the Fine Guidance Sensors of the Hubble Space Telescope. A grid of 105 MK standard as well as ``pathological'' stars guarantees a precise classification. A comparison of our spectral classification with the extensive work of Abt & Morrell (1995, Cat. <J/ApJS/99/135>) shows no significant differences. The derived types are 0.23+/-0.09 (rms error per measurement) subclasses later and 0.30+/-0.08 luminosity classes more luminous than those of Abt & Morrell (1995, Cat. <J/ApJS/99/135>)) based on a sample of 160 objects in common. The estimated errors of the means are +/-0.1 subclasses. The characteristics of our sample are discussed in respect to the distribution on the sky, apparent visual magnitudes and Stromgren uvbybeta colors. Table 2 lists all observed Galactic field stars.
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- ID:
- ivo://CDS.VizieR/J/A+AS/97/951
- Title:
- uvby-beta photometry of metal-poor stars
- Short Name:
- J/A+AS/97/951
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A second catalogue of uvby-beta photometry for 553 high-velocity stars is given; nearly all of these stars come from the Lowell Proper Motion Survey. These data have been taken and reduced using the same photometer, same observing techniques, same standard stars and photometric values, and same reduction programs as the "northern" observations of the first catalogue (Paper I). The errors of these data are very similar to those of the previous catalogue; for most stars the mean errors of V, m1, c1 and beta are less than +/- 0.008 mag., and less than +/- 0.005 mag. for b-y.
- ID:
- ivo://CDS.VizieR/II/180
- Title:
- uvby-beta photometry of metal-poor stars
- Short Name:
- II/180
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the calibrations derived by Schuster and Nissen (=1989A&A...221...65S), the interstellar color excesses, E(b-y), and the metallicities, [Fe/H], have been determined for the 711 high velocity and metal-poor stars in the catalogue of uvby-beta photometry (=1988A&AS...73..225S). 220 of these listed in table1 turn out to be halo stars according to the criterion [Fe/H] <= -1.0. About 15% of the halo stars have colors that are significantly affected by interstellar reddening, i.e. E(b-y) > 0.025. The distributions in the c0-(b-y)0 diagram of the halo stars grouped according to [Fe/H], have well defined turn-off points. From the Teff values of these points a minimum age of 18-20 Gyr for the halo stars is determined. However, this age may be 2-3 Gyr too high due to a possible systematic error in Teff for the stellar models used. Relative ages of 77 halo stars in the turn-off region of the c0-(b-y)0 diagram are derived using the isochrones VandenBerg and Bell (=1985ApJS...58..561V). Assuming that the O/Fe abundance ratio is constant in halo stars, evidence of a cosmic age scatter of +/-2.5Gyr at a given metallicity is found. Furthermore, the mean age of the halo stars is found to decrease smoothly by about 3 Gyr from [Fe/H]= -2.0 to -1.0. These results suggest that a pressure-supported slow uniform collapse controlled the formation and early evolution of the Galaxy. However, the scenario of Searle and Zinn (=1978ApJ...225..357S) is also compatible with the results.
- ID:
- ivo://CDS.VizieR/J/A+AS/117/317
- Title:
- uvby-beta photometry of metal-poor stars. VIII.
- Short Name:
- J/A+AS/117/317
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalogue of uvby-{beta} photometry for 87 of the turn-off and subgiant stars from the HK survey of Beers et al. (1992AJ....103.1987B, BPSII) is given. Most of these stars have [Fe/H]<=2.5. These photometric data have been taken and reduced using the same techniques as in our previous two uvby-{beta} catalogues (Schuster et al., 1989, Cat. <II/180> and Schuster et al., 1993, Cat. <J/A+AS/97/951>). An error analysis has been made; typical mean observational errors for a star with V=14.2m are 0.008, 0.007, 0.011, 0.010 and 0.012 in V, (b-y), m_1_, c_1_ and {beta}, respectively. Our photometric data are also compared to the UBV photometry and spectral indices from the HK survey; satisfactory agreement is found indicating good quality for the two data sets. The stars are classified in reddening-free diagrams of the uvby-{beta} system; several of the stars are found to have been mis-classified in the HK survey. Two metal-poor supergiants, three (possibly four) horizontal branch stars, one blue subluminous star and two stars with ambiguous photometry have been identified. Stellar parameters, such as E(b-y), M_V_, {delta}M_V_, and T_eff_, plus error estimates for these parameters, are provided using our photometric calibrations. Although all stars have galactic latitudes |b|>=30{deg} many of them are significantly reddened with E(b-y) ranging from 0.02 to 0.15. The average reddening towards the South Galactic Pole region, b<-60{deg}, is E(b-y)=0.027+/-0.004 corresponding to E(B-V)=0.036+/-0.005 in contrast to the low value of E(B-V)~0.01 derived from the Burstein & Heiles (1982AJ.....87.1165B) maps. The stars are analyzed in the (b-y)_0_, [Fe/H] diagram, and individual ages estimated using the isochrones of VandenBerg & Bell (1985ApJS...58..561V) and of Bergbusch & VandenBerg (1992ApJS...81..163B). These very metal-poor stars are found to be coeval, within 1-2Gyr, with the halo and thick-disk stars studied previously, with a mean age in excess of 18Gyr. Several blue "thick-disk" stars, which are perhaps analogous to the "blue metal-poor" stars of Preston et al. (1994, Cat. <J/AJ/108/538>), have been identified.
- ID:
- ivo://CDS.VizieR/J/MNRAS/358/66
- Title:
- uvby{beta} photometry of NGC 663
- Short Name:
- J/MNRAS/358/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present CCD uvby{beta} photometry for stars in the central area of the young open cluster NGC 663. We find that the reddening is highly variable, with values ranging from E(b-y)=0.639+/-0.032 in the central part to E(b-y)=0.555+/-0.038 in the south-east. The distance modulus is found to be 11.6+/-0.1mag. (2.1kpc), and the age logt=7.25+/-0.1 years (25+7/-5Myr).
- ID:
- ivo://CDS.VizieR/J/A+AS/104/9
- Title:
- uvby-beta photometry of stars in SA 194
- Short Name:
- J/A+AS/104/9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+AS/100/571
- Title:
- uvby-beta photometry of SX Phe stars
- Short Name:
- J/A+AS/100/571
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/A+AS/145/187
- Title:
- uvby-{beta} photometry of WTTS
- Short Name:
- J/A+AS/145/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present uvby-{beta} photometry of 116 X-ray flux-selected active stars in the directions of the Orion (40), Taurus-Auriga (58) and Scorpius OB2-2 (18) star forming regions. Additionally, we give near IR JHK photometry of 20 active stars in the Taurus-Auriga direction. The program stars were selected from the ROSAT All Sky Survey and EINSTEIN X-ray surveys and are spectroscopically confirmed weak-line T Tauri stars and weak-line T Tauri star candidates. The photometry confirms the young nature of the program stars and also indicates that a significant fraction of the sample could be foreground objects. The data given here probably represent the largest homogeneous uvby-{beta} photometric sample of new WTTS and WTTS candidates. Many objects in the sample are observed photometrically for the first time.
- ID:
- ivo://CDS.VizieR/J/A+AS/123/1
- Title:
- uvbyBeta photometry of ZZ UMa
- Short Name:
- J/A+AS/123/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents first complete uvby light curves of the late-type detached eclipsing binary ZZ UMa (G0V + G8V, P=2.2993d). This binary system has been observed during eight campaigns at the Calar Alto Observatory (Almeria, Spain) and at the Sierra Nevada Observatory (Granada, Spain). 294 points distributed over the binary period and covering both eclipses are given. The comparison stars used to calculate the differential light curves (SAO 15242 and SAO 15251) were confirmed as being good reference stars with constant flux. These observations are part of a 6 year uvby and H{beta} monitoring program of low mass eclipsing binaries whose main objective is to provide accurate absolute astrophysical parameters for late-type main sequence stars. Details about the standardisation process and accuracy of the photometry are also given. The internal accuracy of the standard photometry measured as the mean RMS of the differences between standard and observed values for the standard stars observed along the program is only a few millimagnitudes. Detailed analysis of ZZ UMa, based on these light curves, will be published separately (Clement et al., 1997, Cat. <J/A+AS/123/59>).
- ID:
- ivo://CDS.VizieR/J/AJ/150/134
- Title:
- uvbyCaH{beta} photometry of NGC 752
- Short Name:
- J/AJ/150/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Precision uvbyCaH{beta} photometry of the nearby old open cluster, NGC752, is presented. The mosaic of CCD fields covers an area ~42' on a side with internal precision at the 0.005-0.010mag level for the majority of stars down to V~15. The CCD photometry is tied to the standard system using an extensive set of published photoelectric observations adopted as secondary standards within the cluster. Multicolor indices are used to eliminate as nonmembers a large fraction of the low probability proper-motion members near the faint end of the main sequence, while identifying 24 potential dwarf members between V=15.0 and 16.5, eight of which have been noted before from Vilnius photometry. From 68 highly probable F dwarf members, we derive a reddening estimate of E(b-y)=0.025+/-0.003 (E(B-V)=0.034+/-0.004), where the error includes the internal photometric uncertainty and the systematic error arising from the choice of the standard (b-y,H{beta}) relation. With reddening fixed, [Fe/H] is derived from the F dwarf members using both m_1_ and hk, leading to [Fe/H]=-0.071+/-0.014(sem) and -0.017+/-0.008(sem), respectively. Taking the internal precision and possible systematics in the standard relations into account, [Fe/H] for NGC 752 becomes -0.03+/-0.02. With the reddening and metallicity defined, we use the Victoria-Regina isochrones on the Stromgren system and find an excellent match for (m-M)=8.30+/-0.05 and an age of 1.45+/-0.05Gyr at the appropriate metallicity.
