Uvby Photometry Research Articles

3.23. The centre of the LMC bar

We study star formation and chemical evolution in the LMC Bar centre with the HST PC and uvby photometry. For all bands, mean turn off star data have σ around 0.015 mag. Present data have zero points from stars in M67. b-y of these stars coincides with target turn off. All measurement bands have zero point accuracy better than 0.010 mag.

Uvby photometry of the magnetic chemically peculiar stars HD 37776, HR 2258, HR 6958, and 108 Aquarii

Differential Strömgren uvby photometric observations from the Four College Automated Photoelectric Telescope are presented for four magnetic chemically peculiar stars. Comparison with uvby photometry of Pedersen & Thomsen for HD 37776 yields an improved period of 1.538675 days. New periods of 15.0305 days and 18.065 days are found for the sharp-lined stars HR 2258 and HR 6958, respectively, rather than one of their aliases. For HR 6958 each color shows a slightly different time of maximum. Comparison of the four color photometry of 108 Aqr taken during the fall of 1995 which well covers the period shows the presence of a secondary minimum near primary maximum in u, v, and b. Comparison with published photometry indicates indicates that subtle changes in the shapes of the light curves have occurred suggesting that this star might be precessing.

BVRIJHK PHOTOMETRY OF CEPHEID VARIABLES

ABSTRACT Contemporaneous BVRI and JHK photometry are presented for twenty-two Cepheid variables. Nineteen of these variables also have uvby photometry available, making them excellent candidates for application of the Infrared Flux Method of distance determination. We are in the process of acquiring high precision radial velocities of sixteen of these variables in anticipation of conducting that analysi.

CCD Stromgren Photometry of Young Reddened Clusters

view Abstract Citations (16) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CCD Stromgren Photometry of Young Reddened Clusters Delgado, Antonio J. ; Alfaro, Emilio J. ; Cabrera-Cano, Jesus Abstract The capabilities of CCD uvby photometry for the study of reddened young clusters are investigated. Observations of four fields in the direction of the clusters Basel 1, Berkeley 86, NGC 6704, and NGC 6756, with a total of 1665 stars measured in at least the y and b bands, produce new estimates for the clusters parameters. The results are compared to those from previously published studies in different photometric systems showing good agreement in the values of color excess and distance modulus, with the exception of NGC 6756, for which an essentially larger distance is found. Furthermore, the ages estimated for this cluster, Basel 1, and NGC 6704 are found to be higher than previously assumed, in particular for the last one. The presence of red giants as cluster members is suggested in Basel 1, NGC 6704, and NGC 6756. Publication: The Astronomical Journal Pub Date: February 1997 DOI: 10.1086/118290 Bibcode: 1997AJ....113..713D full text sources ADS | data products SIMBAD (22)

The metallicity distribution of G dwarfs in the solar neighbourhood

We derive a new metallicity distribution of G dwarfs in the solar neighbourhood, using uvby photometry and up-to-date parallaxes. Our distribution comprises 287 G dwarfs within 25 pc from the Sun, and differs considerably from the classic solar neighbourhood distribution of Pagel & Patchett and Pagel by having a prominent single peak around [Fe/H] = -0.20 dex. The raw data are corrected for observational errors and cosmic scatter assuming a deviation of 0.1. In order to obtain the true abundance distribution, we use the correction factors given by Sommer-Larsen, which take into account the stellar scale heights. The distribution confirms the G dwarf problem, that is, the paucity of metal-poor stars relative to the predictions of the simple model of chemical evolution. Another feature of this distribution, which was already apparent in previous ones, is the small number of metal-rich stars again in comparison with the simple model. Our results indicate that it is very difficult to fit the simple model to this distribution, even with the definition of an `effective yield'. A comparison with several models from the literature is made. We find that models with infall are the most appropriate to explain the new metallicity distribution. We also show that the metallicity distribution is compatible with a major era of star formation occurring 5 to 8 Gyr ago, similar to results found by several authors.

Uvby photometry of 100 stars in the region of Carina

uvby photometry of 100 stars in the region of Carina

UVBY AND BETA PHOTOMETRY FOR STARS IN THE OPEN CLUSTER NGC 1502

ABSTRACT New uvby and Beta photoelectric photometry has been obtained for stars in NGC 1502, a young open cluster with relatively high interstellar reddening. It is shown that some of the previous published data for the cluster suffers from small systematic errors. After correction for zero-point differences, the previous data have been combined with the new data and accurate values of the interstellar reddening [E(b-y)=0.54 mag] and distance modulus [(V0-MV=9.71 mag] have been obtained. These are compared with similar values calculated from published UBV photometry and MK spectral types, which agree well with the uvby-Beta analysis. It is found that the reddening is not variable over the cluster field, contrary to previous estimates. The fact that systematic errors exist in precise photometry highlights the importance of a careful selection of standard stars in any photometry of reddened B-type stars.

Reddening estimation for halo red giants using UVBY photometry

view Abstract Citations (92) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Reddening Estimation For Halo Red Giants Using UVBY Photometry Anthony-Twarog, Barbara J. ; Twarog, Bruce A. Abstract Updated uvby observations for a larger sample of metal-deficient red giants are presented and combined with a select sample of data from the literature transformed to a common system. Using the reddening maps of Burstein & Heiles (1982), new absolute magnitudes, distances, metallicities, and reddenings are derived for each star. The metallicities are determined with a revised calibration of the m1, (b-y) diagram based upon comparison to a complilation of recent spectrsoscopic abundances transformed to a common system. The photometric abundances agree very well with the spectroscopic; the dispersion among the residuals for 58 giants is +/- 0.16 dex. The dereddened indices are used to show that for red giants with (Fe/H) less than -1.5, there is a well-defined relation in the c0, (b-y)0 diagram which exhibits only a weak dependence upon metallicity. Use of the standard relations allows one to obtain reddening estimates for normal halo field giants and globular clusters in the appropriate metallicity range. Publication: The Astronomical Journal Pub Date: April 1994 DOI: 10.1086/116969 Bibcode: 1994AJ....107.1577A Keywords: Galactic Evolution; Globular Clusters; Halos; Interstellar Extinction; Photometry; Red Giant Stars; Spectroscopy; Stellar Magnitude; Astronomical Catalogs; Geomagnetic Latitude; Luminosity; Metallicity; Northern Sky; Astronomy; STARS: GIANT; GALAXY: HALO; STARS: ABUNDANCES full text sources ADS | data products SIMBAD (140) GCPD (1) Related Materials (1) Catalog: 1994yCat..51071577A

Simultaneous photometry and spectroscopy of the rapid variability of the Be star η Cen

The reality of the previously reported triple-wave light curve (Cuypers et al. 1989, A&A Suppl. 81, 151), and relations between rapid line profile and brightness variations of the B1-2III-Ve star η Cen (HD 127972) were investigated by means of simultaneous high-resolution spectroscopy (4 nights, 86 Si III 455.2622 nm profiles) and two-station uvby photometry (14 nights) secured in 1992. To this database were added the uvby photometry by Cuypers et al. and unpublished b observations by L.A.B. from 1988–1991.

Goodbye to Polaris the Cepheid

view Abstract Citations (30) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Goodbye to Polaris the Cepheid Fernie, J. D. ; Kamper, Karl W. ; Seager, S. Abstract New radial velocities and uvby photometry for Polaris are presented. These reveal that the pulsational amplitude of Polaris had declined to 0.59±0.19 km s-1 and 0.010±0.002 mag in V by 1992. Comparison with earlier determinations reveals an exponential change with time rather than any sudden onset of the decline, and suggests that Polaris had an amplitude near 0.12 mag (6.0 km s 1) prior to 1900. There is no sign of the amplitude changing in a manner consistent with a beat phenomenon; instead, the star seems destined to stop pulsating in 1994. Our data add new points to the O-C diagram of Polaris and show a continuation of the period increase known previously. We point out that departures of this diagram from a true parabola do not necessarily imply that factors other than stellar evolution are at work. Finally, we lay to rest the myth that the amplitude of Polaris has declined because it is evolving across the red edge of the Cepheid instability strip. We show Polaris to be well within the strip and surrounded there by Cepheids of substantial amplitude. In particular, Polaris is virtually identical to RT Aur in MV and color, yet RT Aur has an amplitude of 0.8 mag. We conclude that there is as yet no adequate understanding of what sets the amplitude of a Cepheid Publication: The Astrophysical Journal Pub Date: October 1993 DOI: 10.1086/173279 Bibcode: 1993ApJ...416..820F Keywords: Cepheids -- stars: individual (α Ursae Minoris) full text sources ADS | data products SIMBAD (5)

The abundance of lithium in metal-poor subgiant stars

We have determined lithium abundances for a sample of 79 halo subgiants. The subgiant candidates were identified using uvby photometry from several catalogs of metal-poor stars. The basic data were high-resolution, low-noise coude spectra in the 6700 A spectral region. Abundances of iron and calcium, derived from one Ca I and several Fe I lines in our spectra, provided a metallicity discriminant for the stars in our sample. The subgiants with temperatures between 5500 and 4900 K show a steady decline of lithium abundance with advancing subgiant position (and decreasing temperature). The observed trend is in qualitative agreement with recent theoretical models of lithium dilution in metal-poor stars, especially if main-sequence diffusion is included

UBV and UVBY photometry of the magnetic CP star 56 ARIETIS - 1990 and 1991

UBV and uvby photometry of the magnetic CP Star 56 Arietis from the Braeside Observatory and the Four College Automated Photoelectric Telescope, respectively, significantly differs from previously published values. Observations with each filter taken in the fall of 1990 show small differences in the shapes of the light curves compared with similar observations a year later. A possible explanation consistent with the radiative diffusion model for such stars is that we are observing a free body precession of a spotted star. As there is now clear evidence that the light curves of at least one CP star do change, it is desirable to continue these observations to see if these changes are periodic albeit that the period may be of order of a decade for 56 Ari

Age Determination for Am Stars

AbstractFrom uvby and Hβ photometry, individual stellar ages for A type stars have been derived using three different evolutionary models. In this paper we evaluate the corrections for metallicity and rotation to be applied to the physical parameters of Am and their influence on the determined ages. A test based on the Hyades open cluster is also presented.

28 And: Simultaneous Strömgren Photometry

AbstractWe have carried out simultaneous uvby photometry of the low amplitude δ Set star 28 And. Analysis of the data, using the Fourier Transform method, establishes 28 And as a monoperiodic pulsator. Using the classical O-C method, it is found that the pulsation of this star can be well described by means of a linear ephemeris with a period of P=0.d069304118 over the last twenty-four years. Amplitude variations are also shown to be present from season to season. The physical parameters of this star are determined and the nature of radial or nonradial pulsation is discussed on the basis on the derived phase shifts and amplitude ratios between Strömgren colours. The results indicate that 28 And pulsates in a nonradial mode with ℓ = 2.

PHOTOELECTRIC OBSERVATIONS OF SOME BRIGHT BE STARS

ABSTRACT Differential Stromgren uvby photometry of several bright Be stars obtained with the Four College Automated Photoelectric Telescope are presented both to examine the quality of data obtained with this telescope and to study the variability of these stars during 1990-91.

Secondary uvby standards in the Harvard E-regions

Photoelectric uvby photometry for 201 stars which are already UBV (RI) c standards are presented. The photoelectric data are closely tied to the Cousins uvby standards and the stars should be suitable for use as fainter (7-11 mag) secondary standards

Strømgren Photometry of Wide Visual Double Stars with G–Type Primaries, Most of Which Have Common Origin Components

AbstractWe have performed uvby aperture photometry of wide visual double stars with G–type primaries. We chose our pairs in order to have minimum angular separation of their components 10″ and mainly less than 20″. It is shown that both components have similar photometric parameters. We infer that most of these double stars have components of common origin.

Near-infrared and Stromgren photometry of the open clusters NGC 663, NGC 1502 and NGC 1893*

Near-infrared JHK, and Stromgren uvby and Hβ photometry of the central parts of three open clusters, NGC 663, NGC 1502 and NGC 1893, are presented. The following results were derived from the data : NGC 663 is at a distance of 2.5 kpc (m−M=12.03±0.20) and is obscured by A v =1.98±0.04, its age is 9×10 6 yr; NGC 1502 is at a distance of 1.5 kpc (m−M=10.84±0.10) and is obscured by A v =1.83±0.03, its age is 5×10 6 yr; NGC 1893 is at a distance of 4.3 kpc (m−M=13.18±0.11) and is obscured by A v =1.68±0.06, its age is 4×10 6 yr.

AN INVESTIGATION OF THE SPECTROSCOPIC-VISUAL TRIPLE SYSTEM 20 LEONIS

ABSTRACT Stromgren uvby photometry of the spectroscopic-visual triple system 20 Leonis was obtained at Mount Laguna Observatory of San Diego State University. The delta Scuti visual component was found to have only one period of 0.0826 day, although another may be present in the data. The spectroscopic binary component was found to undergo grazing eclipses from which an inclination of 75 ± 1 deg was tentatively determined. Radial velocities obtained from the Dominion Astrophysical Observatory 1.2-m telescope were combined with Fekel and Bopp's 1977 velocities, and new orbital elements were calculated. Spectroscopic observations of the visual component also showed that there has been an observable change in the system since 1977. The possibility that this system may be an ellipsoidal variable rather than an eclipsing binary was also investigated.

The Cape rapidly oscillating Ap star survey - I. First results

We present the first results of a systematic survey of the roAp phenomenon in the southern hemisphere. The scientific goals of the survey are; (i) to increase the number of known roAp stars so that the extent of the roAp phenomenon can be better determined; (ii) to apply the techniques of asteroseismology to these new roAp stars; (iii) to study the relationship between the roAp stars and other pulsating stars, particularly the |$\delta$| Scuti stars which lie in the same region of the HR diagram. Our initial goal is to obtain a complete catalogue of Strömgren uvby and Hβ photometry of the Ap SrCrEu stars listed in the four currently available volumes of the Michigan Spectral Catalogue of the HD stars. The survey currently extends as far north as |$\delta=-12$|˚. In this declination range we have identified 464 Ap SrCrEu stars which comprise our primary list of candidates. This list is supplemented by a further 71 candidates with |$\delta\gt-12$|˚ drawn from the list of Ap stars by Bidelman & MacConnell. Thus far we have obtained at least one |$u\nu by\beta$| observation of 51 per cent of our candidates. Stars are then selected for follow-up observations with high-speed photometry on the basis of the similarity of their |$b-y,m_1,c_1$| and β indices to those of the known roAp stars. The efficacy of our technique is such that we are able to present here five new rapidly oscillating Ap stars which were discovered on 10 photometric nights spanning one month. These are as follows, (i) HD 161459. which oscillates with several periods near 12.0 min although the severity of the aliases in our amplitude spectra is such that we are able only to determine the principal oscillation frequency |$\nu_1=1.39$| mHz. (ii) HD 190290 which shows oscillatory behaviour reminiscent of that seen in the rich multi-model pulsator HR 1217. We demonstrate the presence of oscillatioas with frequencies at |$\nu_1=2.27$| mHz (p = 7.34 min) and |$\nu_2=2.23$| (P = 7.47 min) and we argue that these must be two excited p-modes. Other oscillation frequencies are also indicated. (iii) HD 196470, an equatorial Ap SrEu(Cr) star which oscillates with a 10.79-min period, (iv) HD 193756, which oscillates with a 12.98-min period, (v) HD 218495, a hot (β = 2.87) roAp star which oscillates with a period of 7.44 min. There is also an indication of the presence of the first harmonic of the principal oscillation frequency.