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The Calibration of the Swift UVOT Optical Observations: A Recipe for Photometry
The Ultraviolet/Optical Telescope (UVOT) on board Swift has thecapability to provide critical insight into the physics of the earlyafterglows of gamma-ray bursts (GRBs). But without precise calibrationof the UVOT to standard photometric systems, it is impossible toleverage late-time, ground-based follow-up data to the early-time UVOTobservations. In this paper, we present a calibration of the Swift UVOTphotometry to the standard Johnson UBV system for the UVOT U, B, and Vfilters, and a step-by-step photometry recipe for analyzing these data.We base our analysis on aperture photometry performed on theground-based and UVOT observations of the local standard stars in thefields of supernovae (SNe) 2005am and 2005cf and a number of Landoltstandard stars. We find that the optimal photometry aperture radius forUVOT data is small (2.5" for unbinned data, 3.0" for 2×2 binneddata), and we show that the coincidence-loss (C-loss) correction isimportant even for relatively faint magnitudes (16-19 mag). Based on atheoretically motivated model, we fit the C-loss correction with twoparameters, the photometric zero point (ZP) and the saturation magnitude(m&infy;), and derive tight constraints for both parameters[σ(ZP)=0.01 mag and σ(m&infy;)=0.02 mag)]. Wefind that the color-term correction is not necessary for the UVOT B andV filters but that it is necessary for the U filter for blue objects[(U-V)<0.4 mag]. We analyze the UVOT UBV photometry of SN 2005am andfind that the UVOT photometry is generally consistent with theground-based observations but that a difference of up to 0.5 mag isfound when the SN became faint. We also apply our calibration results tothe UVOT observations of GRB 050603. There is a scatter of ~0.04-0.08mag in our final UVOT photometry, the cause of which is unclear, but itmay be partly due to the spatial variation in the pixel sensitivity ofthe UVOT detector.
| 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.
| Absolute magnitudes for late-type dwarf stars for Sloan photometry
We present a new formula for absolute magnitude determination forlate-type dwarf stars as a function of (g-r) and (r-i) for Sloanphotometry. The absolute magnitudes estimated by this approach arebrighter than those estimated by colour-magnitude diagrams, and theyreduce the luminosity function rather close to the luminosity functionof Hipparcos.
| Optical and Infrared Photometry of the Nearby Type Ia Supernovae 1999ee, 2000bh, 2000ca, and 2001ba
We present near-infrared photometry of the Type Ia supernova (SN)1999ee; also, optical and infrared photometry of the Type Ia SNe 2000bh,2000ca, and 2001ba. For SNe 1999ee and 2000bh, we present the first-everSN photometry at 1.035 μm (the Y band). We present K-corrections thattransform the infrared photometry in the observer's frame to thesupernova rest frame. Using our infrared K-corrections and stretchfactors derived from optical photometry, we construct JHK templates thatcan be used to determine the apparent magnitudes at maximum if one hassome data in the window -12 to +10 days with respect toT(Bmax). Following up previous work on the uniformity of Vminus IR loci of Type Ia supernovae of midrange decline rates, wepresent unreddened loci for slow decliners. We also discuss evidence fora continuous change of color at a given epoch as a function of declinerate.
| 15 colour photometry of the Landolt SA95 standard star field
In this paper, we present a set of photometric observations in 15 colorsof stars in the Landolt SA95 field with the BATC system. The wavelengthscovered by the system range from 300 nm to 1000 nm. Visual magnitudes ofthe stars studied in the field are from the 10th to 20th mag. Theobservational methodology and the data reduction procedures aredescribed. The relationships between the BATC intermediate-band systemand the Landolt UBVRI broad band system are obtained. A catalogue of thephotometry has been produced which contains the SEDs of 3613 stars. Thework is partly supported by Chinese National Sciences Foundation underthe contract No. 19833020 and No. 19503003. The catalogue is onlyavailable at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/361
| The u'g'r'i'z' Standard-Star System
We present the 158 standard stars that define the u'g'r'i'z' photometricsystem. These stars form the basis for the photometric calibration ofthe Sloan Digital Sky Survey. The defining instrument system andfilters, the observing process, the reduction techniques, and thesoftware used to create the stellar network are all described. Webriefly discuss the history of the star selection process, thederivation of a set of transformation equations for theUBVRCIC system, and plans for future work.
| Photometric catalog of nearby globular clusters. I. A large homogeneous (V,I) color-magnitude diagram data-base
We present the first part of the first large and homogeneous CCDcolor-magnitude diagram (CMD) data base, comprising 52 nearby Galacticglobular clusters (GGC) imaged in the V and I bands using only twotelescopes (one for each hemisphere). The observed clusters represent75% of the known Galactic globulars with (m-M)_V<= 16.15 mag, covermost of the globular cluster metallicity range (-2.2 <= [Fe/H]<=-0.4), and span Galactocentric distances from ~ 1.2 to ~ 18.5 kpc. Inthis paper, the CMDs for the 39 GGCs observed in the southern hemisphereare presented. The remaining 13 northern hemisphere clusters of thecatalog are presented in a companion paper. For four clusters (NGC 4833,NGC 5986, NGC 6543, and NGC 6638) we present for the first time a CMDfrom CCD data. The typical CMD span from the 22nd V magnitudeto the tip of the red giant branch. Based on a large number of standardstars, the absolute photometric calibration is reliable to the ~ 0.02mag level in both filters. This catalog, because of its homogeneity, isexpected to represent a useful data base for the measurement of the mainabsolute and relative parameters characterizing the CMD of GGCs. Basedon data collected at the European Southern Observatory, La Silla, Chile.
| Relative Fluxes by Spectrophotometry with RUBIKON
By means of the RUBIKON multi-channel detector system with integratedgrism spectrograph, attached to the Bochum 61cm telescope, five primarystandars stars have been intercompared and an additional secondarystandard star (HD 37027 in the center field of the LMC) has been set upin the wavelength range of 326-777 nm.
| Quantitative spectral classification of galactic disc K-M stars from spectrophotometric measurements
New spectral observations for 47 southern galactic red supergiantsobtained with the new RUBIKON spectrophotometer (developed at theAstronomisches Institut der Ruhr-Universitat Bochum) at the Bochum 61-cmtelescope on La Silla are presented. The spectra range from 4800 to 7700A and their resolution is 10 A. The mean error of absolute fluxes is0.028 mag and that of relative fluxes 0.021 mag. The spectra will beavailable at the Strasbourg Stellar Database (CDS). Together with datataken from recently published spectral catalogues, the new observationshave been used to define spectral indices as measures of the strengthsof the following features: Fe i+TiOalpha_1, Mgb+TiOalpha_0,NaD+TiOgamma'_1, TiOgamma'_0 and TiOgamma_1 systems. The indices havebeen checked against errors introduced by reductions, interstellarreddening and different resolutions of different spectral catalogues,and have been found to be very insensitive to all these effects.Therefore, different catalogues may be combined without any loss ofaccuracy and homogeneity. The mean error of a single index has beenfound to be 0.011 mag. For stars from K4 to M7, a strong temperaturedependence is found for all indices. For the Fe i+TiO and especially theMgb+TiO features, a strong dependence on luminosity has also beenobserved. These indices therefore have been combined to form aluminosity index, while the others together form a spectral index. Thecombined indices have been calibrated in terms of MK data using thestepwise linear regression technique, and may be used for quantitativetwo- dimensional spectral classification of late K- and M-type stars.The mean error of the classification is 0.6 of spectral subtype and 0.8of luminosity class, which is much higher than would be expected fromthe uncertainty of the indices alone (which, e.g., for an M4 giantcorrespond to an uncertainty of 0.1 of spectral subtype and 0.3 ofluminosity class). This may be explained by the uncertainty of theoriginal MK classifications and the variability of some programme stars.
| 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.
| UBVRI photometric standard stars in the magnitude range 11.5-16.0 around the celestial equator
UBVRI photoelectric observations have been made on theJohnson-Kron-Cousins photometric system of 526 stars centered on thecelestial equator. The program stars within a 298 number subset havesufficient measures so that they are capable of providing, fortelescopes of intermediate and large size in both hemispheres, aninternally consistent homogeneous broadband standard photometric systemaround the sky. The stars average 29 measures each on 19 nights. Themajority of the stars in this paper fall in the magnitude range11.5-16.0, and in the color range -0.3 to +2.3.
| 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.
| Spectrophotometry of stars of intermediate brightness
Spectrophotometric observations of 15 stars in a magnitude range m ofbetween 8.0 and 10.9, located mostly near the equator and covering allthe range of right ascensions, are presented. The energy distributionshave been obtained in Hayes' (1970) system as revised by Hayes andLatham (1975), and in the augmented system presented by Taylor (1984).Comments about some of the standard stars are presented as well as acomparison of the results obtained with both systems.
| 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.
| Distances to eclipsing binaries. III - Masses, radii, and absolute magnitudes of 96 stars
Distances to, and absolute magnitudes of, 96 components of eclipsingbinaries with well-determined absolute dimensions have been computedusing V-R photometry. The calculations take into account interstellarreddening, which is estimated from existing UBV and uvby-betaphotometry, as well as photometric proximity effects. The resultingabsolute magnitudes, dimensions, and masses are compared with zero-agemain sequences predicted by theory. Theory is in good agreement with theobserved data for stars more massive than the sun if a composition (X,Y, Z) = (0.66 + or - 0.03, 0.303 + or - 0.03, 0.037 + or - 0.005) ischosen. The corresponding helium-to-hydrogen number ratio is 0.115 + or- 0.02, in agreement with previous estimates.
| 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
| A set of faint equatorial standard stars for BVRI photometry
BVRI photoelectric photometry is presented for 48 of Landolt's (1973)faint equatorial standard stars. The 48 stars, which have spectral typesfrom A to K and V magnitudes in the range from 8.0 to 12.0, are chosento provide two blue and two red stars in each of 12 of the equatorialselected areas studied by Landolt. The program stars were observed withan S-1 photomultiplier, with the B-V, V-R, and V-I colors transformed tothe Johnson system; they were also observed with an RCA 31034Aphotomultiplier, with the resulting V-R and V-I colors given on azero-point-adjusted instrumental system. Observations of several Mdwarfs with the two photomultipliers are also reported. Serious problemsencountered in transforming the observed V-R and V-I colors of the Mdwarfs to the Johnson system are discussed.
| 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.
| Photoelectric UBV photometry of stars in ten Selected Areas
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973MNRAS.164..121P&db_key=AST
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Observation and Astrometry data
| Constellation: | Eridanus |
| Right ascension: | 03h52m54.19s |
| Declination: | +00°00'18.8" |
| Apparent magnitude: | 10.091 |
| Proper motion RA: | 13.8 |
| Proper motion Dec: | -1.6 |
| B-T magnitude: | 10.229 |
| V-T magnitude: | 10.103 |
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