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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.
| Photometric Variability of the Gravitational Lens 0142-100 (UM 673)
We present the results of a photometric CCD monitoring of thegravitational lens system UM 673 that took place from 1995 to 2000. Intotal, the doubly imaged quasar (QSO) was observed in the R band during29 photometric nights, using optical telescopes with dimensions in therange 0.6-1.3 m. We detected a significant variability in the totallight of the UM 673 system, that is, in the light of the two QSO imagesplus the lensing galaxy. With respect to the magnitude of thegravitational lens system at its discovery, in 1986, UM 673 was 0.3 magbrighter. Furthermore, our 1996 December measurements show that between1995 November and 1997 October the system became even brighter, reachinga magnitude difference of 0.5 mag with respect to its discovery value.We also present R magnitudes and V-R colors of seven field starssituated in the vicinity of the lens, based on a 3.5 month monitoringduring the year 2000. Based on observations made with (1) the 60 cmBochum and the ESO 90 cm Dutch telescopes, at La Silla, Chile, (2) the1.2 m telescope at Kryonerion Observatory, Greece, (3) the 1.3 mtelescope at Skinakas Observatory, Crete, Greece, and (4) the EuropeanSpace Agency OGS telescope operated on the island of Tenerife by theInstituto de Astrofísica de Canarias in the Spanish Observatoriodel Teide of the Instituto de Astrofísica de Canarias.
| Is It Round? Spectropolarimetry of the Type II-p Supernova 1999EM
We present the first multiepoch spectropolarimetry of a Type II plateausupernova (SN II-P), with optical observations of SN 1999em on days 7,40, 49, 159, and 163 after discovery. These data are used to probe thegeometry of the electron scattering atmosphere before, during, and afterthe plateau phase, which ended roughly 90 days after discovery. Weakcontinuum polarization with an unchanging polarization angle(θ~160deg) is detected at all epochs, with p~0.2% onday 7, p~0.3% on days 40 and 49, and p~0.5% in the final observations.Distinct polarization modulations across strong line features arepresent on days 40, 49, 159, and 163. Uncorrected for interstellarpolarization (which is believed to be quite small), polarization peaksare associated with strong P Cygni absorption troughs, and nearlycomplete depolarization is seen across the Hα emission profile.The temporal evolution of the continuum polarization and sharp changesacross lines indicate polarization intrinsic to SN 1999em. When modeledin terms of the oblate, electron scattering atmospheres of Höflich,the observed polarization suggests an asphericity of at least 7% duringthe period studied. The temporal polarization increase may indicategreater asphericity deeper into the ejecta. We discuss the implicationsof asphericity on the use of Type II-P supernovae as primaryextragalactic distance indicators through the expanding photospheremethod (EPM). If asphericity produces directionally dependent flux andpeculiar galaxy motions are characterized byσvrec=300 km s-1, it is shownthat the agreement between previous EPM measurements of SNe II anddistances to the host galaxies predicted by a linear Hubble lawrestricts mean SN II asphericity to values less than 30% (3 σ)during the photospheric phase.
| Young stars and scattered light in the powerful radio galaxy 3C 321
Blue spectropolarimetry observations are presented for the low-redshiftradio galaxy 3C 321 (z=0.096). The percentage polarization is found toshow a spectacular decline from the UV to the optical - by a factor of 5from the shortest to the longest wavelengths covered by the observations- and the polarization angle is within 15 deg of the perpendicular tothe radio axis. These results are consistent with the presence of ascattered AGN component which comprises 20-70 per cent of the UVcontinuum, but is diluted by the light of the old stellar populations atoptical wavelengths. Attempts to model the continuum spectral energydistribution in terms of quasar+E-galaxy or power-law+E-galaxy producegenerally good fits over much of the spectrum, but there is asignificant excess over the models in the rest-wavelength range3900-4300 A. This excess, and the detection of the higher order Balmerlines in absorption, provides strong evidence for the presence of apopulation of young (A-type) stars. The best-fitting model comprises acombination of a quasar, a 1-Gyr starburst, a 15-Gyr-old stellarpopulation and nebular continuum, with these components contributing 22,34, 34 and 10 per cent of the total flux at 3639A respectively. Overall,our results serve to emphasize the multicomponent nature of theoptical/UV continuum of powerful radio galaxies.
| The Hubble Space Telescope Northern-Hemisphere grid of stellar polarimetric standards
Results are presented from a comprehensive program of opticalpolarimetry of strongly polarized and null-polarization standard stars.Potential sources of systematic error either instrumental in origin ordue to absolute calibration are critically discussed. Although theproject emphasized the requirements of a spaceborne optical-UVobservatory (HST), the resulting grid of standards represents a distinctimprovement over previous such tabulations and offers an opportunity toreference future multiwavelength polarimetry to a common system.
| 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.
| An atlas of Hubble Space Telescope photometric, spectrophotometric, and polarimetric calibration objects
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99.1243T&db_key=AST
| UBV Photometry of Equatorial Stars
Not Available
| 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.
| Mean absolute magnitude of the blue stars at high galactic latitude.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962AJ.....67..740K&db_key=AST
| Micrometer Measures of Double Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1959ApJS....4...45V&db_key=AST
| A search for blue stars in high galactic latitudes.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958AJ.....63..484C&db_key=AST
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | לויתן |
| התרוממות ימנית: | 01h57m56.14s |
| סירוב: | -02°05'57.7" |
| גודל גלוי: | 8.845 |
| מרחק: | 467.29 פארסק |
| תנועה נכונה: | 0.6 |
| תנועה נכונה: | -1.1 |
| B-T magnitude: | 8.795 |
| V-T magnitude: | 8.841 |
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