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An Atlas of Spectrophotometric Landolt Standard Stars
We present CCD observations of 102 Landolt standard stars obtained withthe Ritchey-Chrétien spectrograph on the Cerro TololoInter-American Observatory 1.5 m telescope. Using stellar atmospheremodels, we have extended the flux points to our six spectrophotometricsecondary standards, in both the blue and the red, allowing us toproduce flux-calibrated spectra that span a wavelength range from 3050Å to 1.1 μm. Mean differences between UBVRI spectrophotometrycomputed using Bessell's standard passbands and Landolt's publishedphotometry were determined to be 1% or less. Observers in bothhemispheres will find these spectra useful for flux-calibrating spectra,and through the use of accurately constructed instrumental passbands,will be able to compute accurate corrections to bring instrumentalmagnitudes to any desired standard photometric system (S-corrections).In addition, by combining empirical and modeled spectra of the Sun,Sirius, and Vega, we calculate and compare synthetic photometry toobserved photometry taken from the literature for these three stars.
| New pulsational properties of eight `anomalous' RR Lyrae variables
CCD photometry in the V band is presented for seven field RR Lyrae starsselected from a sample of eight variables; these, according to datacollected in the literature, are expected to be ab-type pulsators, tohave short periods (and hence high metallicity), and to be located at ahigh z from the Galactic plane. New periods and epochs are derived forthem. The new periods are only slightly shorter than the valuespublished in the fourth edition of the General Catalogue of VariableStars (GCVS4). In six cases our amplitude of the light variation issignificantly smaller than that published in the GCVS4, and in at leastthree cases the actual pulsation appears to be in the first harmonicrather than in the fundamental mode. All the suggested c-type pulsatorsshow variations in the amplitude and/or quite scattered light curves.Some possible explanations are given. From a spectrophotometric analysisof the sample, only DL Com is confirmed to pulsate in the fundamentalmode, to have a short period, and to be located at a relatively high z.However, a single object cannot be taken as evidence for a significantmetal-rich population at a large distance from the Galactic plane.
| Secondary photometric standard stars for the Thuan-Gunn and Johnson-Kron-Cousins systems
CCD photometry is presented for 119 stars observed in the Thuan-Gunnphotometric system (the passbands vgr). The sample includes 82 stars forwhich magnitudes in this system have not previously been published.Photometry in the Johnson-Kron-Cousins photometric system (BV or UBV)has been obtained for a subsample of 85 of the stars. Of those starswhich are not primary standard stars for the Thuan-Gunn system 70observed in Gunn r, 48 observed in Gunn g, and 37 observed in Gunn vhave sufficient repeat measurements that they may be used as secondarystandard stars for CCD photometry. The typical uncertainties for themagnitudes of these stars are 0.006 mag.
| On the sytematic accuracy of the equatorial UBVRI standard stars
The considerable systematic difference in B-V between northern andsouthern measurements of the equatorial UBVRI standard stars arestudied. It is found that the northern data (Landolt 1983) are muchcloser to the original UBV system than the southern ones. The situationis less clear in the case of V and U-B.
| V803 Aquilae: A newborn W Ursae Majoris Siamese twin?
A complete photometric analysis of BVRI photometry of the physicallycompact, eclipsing binary V803 Aquilae is presented. Six mean epochs ofminimum light were determined from observations covering three primaryand three secondary eclipses. A period study covering 54 years ofobservation or nearly 77,000 orbital revolutions reveals three distincteras of constant period with two major period jumps of +0.1 s and -0.3s. The light curves shows that the primary and secondary eclipse depthsare identical in V, and are nearly identical in B, R, and I, indicatingthat the components have nearly the same temperatures. Standardmagnitudes were determined and a reddening estimate was made. Asimultaneous solution of the four light curves was computed using theWilson-Devinney synthetic light-curve code. The solution indicates thatthe system consists of twin approximately K4 stars in shallow contactwith a fill-out of approximately 8%. A mass ratio of 1.000 was computedwith a negligible temperature difference of only 6 K. Thus, based on ourpurely photometric solution, V803 Aql is made up of 'Siamese' (contact)twin components. Theory would indicate that the twins have just recentlycome into contact, and the lack of other equal-mass W Ursae Majorissystems would indicate that it is in a very transient or unusual state.
| Photometric investigation of a very short period W UMa-type binary - Does CE Leonis have a large superluminous area?
A complete photometric analysis of BVRI Johnson-Cousins photometry ofthe high northern latitude galactic variable, CE Leo is presented. Theseobservations were taken at Kitt Peak National Observatory on May 31,1989-June 7, 1989. Three new precise epochs of minimum light weredetermined and a linear and a quadratic ephemeris were computed fromthese and previous data covering 28 years of observation. The lightcurves reveal that the system undergoes a brief 20 min totality in theprimary eclipse, indicating that CE Leo is a W UMa W-type binary. Asystemic velocity of about -40 km/s was determined. Standard magnitudeswere found and a simultaneous solution of the B, V, R, I light curveswas computed using the new Wilson-Devinney synthetic light curve codewhich has the capability of automatically adjusting star spots. Thesolution indicates that the system consists of two early K-type dwarfsin marginal contact with a fill-out factor less than 3 percent. Evidencefor the presence of a large (45 deg radius) superluminous area on thecooler component is given.
| CCD surface photometry for E and S0 galaxies in the Coma cluster
The paper presents CCD surface photometry in Johnson B and Gunn r for 33galaxies in the Coma cluster and for 13 galaxies in the field or inother clusters, obtained with the Danish 1.54-m telescope at the ESO, LaSilla, Chile in the period April 3-10, 1989. The data were calibratedwith standard stars. Data for all galaxies include derivations ofeffective radius, mean surface brightness, and total magnitude. Goodagreement was found between the photometry and the global parameterspresented with data of Dressler, Faber, Burstein and theircollaborators, indicating that the quality of the CCD data is fullyadequate for studies of the large-scale motions in the universe.
| UBV(RI)c photometry of equatorial standard stars - A direct comparison between the northern and southern systems
UBV(RI)c photometry of 212 stars from Landolt's list of equatorialstandards is presented. The observations are tied to the system definedby Cousin's E-region standards. A comparison of the present results withLandolt's reveals reasonably good agreement for (V-R)c and (V-I)c, butmarked systematic differences for (B-V) and (U-B). The UBV systems ofCousins and Landolt are evidently not the same and both probably differfrom Johnson's original system.
| The 77-81 intermediate-band photometric system
The 77-81 intermediate-band photometric color system for the study oflate-type stars is defined. The passbands are centered on a region ofTiO absorption at 7750 A (77) and on a region of CN absorption at 8100 A(81). Good agreement is found between measurements made on the 77-81system with different detectors. The 77-81 color is well correlated withM type and reasonably correlated with carbon-richness class. The 77-81,V-I color-color diagram clearly distinguishes M and C types from otherstars. It is also shown that the 77-81 color may be used to measure TiOband strength.
| UBVRI photometric standard stars around the celestial equator
It is pointed out that accurate, internally consistent, and readilyaccessible standard star photometric sequences are necessary for thecalibration of the intensity and color data which astronomers obtain atthe telescope. The photometric results provided in connection with thepresent study represent the first part of an effort which is concernedwith the presentation of UBVRI photoelectric photometric standard starsin the magnitude range from 7 to 17 over as broad a range in color aspossible. All of the photometric observations were made with a 31034type photomultiplier used in a pulse counting mode. Some 15 to 25standard stars chosen from Cousins' lists (1973, 1976) in the E-regionswere observed with an 0.4-m telescope each night along with the programstars. UBVRI standard stars were observed periodically throughout thenight. Observations with a 0.9-m telescope were also conducted. TheUBVRI photoelectric observations take into account 223 stars.
| The globular cluster system of the Galaxy. I - The metal abundances and reddenings of 70 globular clusters from integrated light measurements
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980ApJS...42...19Z&db_key=AST
| Spectral classifications for Landolt's celestial equatorial standard stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979AJ.....84..783D&db_key=AST
| Equatorial UBVRI photoelectric sequences
From 1335 BVRI observations of 189 stars in selected areas 92-115,Landolt's (1973) network of faint UBV standards has been extended to RI. Of these stars, 173 have four or more observations. The (U-B) valuesof Landolt are adopted, and a well-observed equatorial faint-starnetwork is presented on the Johnson UBVRI photometric system.
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Virgo |
| Ascensió Recta: | 13h36m43.99s |
| Declinació: | -01°15'38.1" |
| Magnitud Aparent: | 8.361 |
| Distancia: | 456.621 parsecs |
| Moviment propi RA: | 12.3 |
| Moviment propi Dec: | -9 |
| B-T magnitude: | 9.681 |
| V-T magnitude: | 8.47 |
Catàlegs i designacions:
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