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Discovery of the Optical Counterpart and Early Optical Observations of GRB 990712
We present the discovery observations of the optical counterpart of thegamma-ray burst GRB 990712 taken 4.16 hr after the outburst and discussits light curve observed in the V, R, and I bands during the first ~35days after the outburst. The observed light curves were fitted with apower-law decay for the optical transient (OT), plus an additionalcomponent that was treated in two different ways. First, the additionalcomponent was assumed to be an underlying galaxy of constant brightness.The resulting slope of the decay is0.97+0.05-0.02, and the magnitudes of theunderlying galaxy are V=22.3+/-0.05, R=21.75+/-0.05, and I=21.35+/-0.05.Second, the additional component was assumed to be a galaxy plus anunderlying supernova with a time-variable brightness identical to thatof GRB 980425, appropriately scaled to the redshift of GRB 990712. Theresulting slope of the decay is similar, but the goodness of fit isworse, which would imply that either this GRB is not associated with anunderlying supernova or the underlying supernova is much fainter thanthe supernova associated with GRB 980425. The galaxy in this case isfainter: V=22.7+/-0.05, R=22.25+/-0.05, and I=22.15+/-0.05, and the OTplus the underlying supernova at a given time is brighter. Measurementsof the brightnesses of the OT and the galaxy by late-time Hubble SpaceTelescope observation and ground-based observations can thus assess thepresence of an underlying supernova. Based on observations collected atSAAO, Sutherland; ESO, Paranal and La Silla (ESO Programs 63.O-0618 and63-O-0567) and AAT, Australia.
| GRB 990712
IAUC 7225 available at Central Bureau for Astronomical Telegrams.
| On the distance to the Chamaeleon I and II associations
Constraints on the distances to the dark clouds Chamaeleon I and II areinvestigated in detail. A compilation of photometric data, spectraltypes and absolute magnitudes for field stars towards each cloud ispresented, and results are used to examine the distribution of reddeningwith distance along each line of sight. The distances to starsassociated with reflection nebulae in each cloud are examined in detail.On the basis of these results, we deduce the most probable distance ofCha I to be 160+/-15pc, and that of Cha II to be 178+/-18pc. Anexamination of the mean fluxes of T Tauri stars in each cloud providesindependent evidence to suggest that Cha II is significantly moredistant than Cha I. Both clouds appear to be embedded in a macroscopicsheet-like structure extending over much of the Chamaeleon-Musca-Cruxregion. The Chamaeleon III and DC\ts 300.2--16.9 clouds are probablypart of the same structure, with probable distances ~ 140--160pc.
| Four-colour UVBY and H-beta photometry of all stars earlier than G0 and brighter than MPG of about 10.7 M in Selected Area 203 towards the Chamaeleon-Musca dark clouds
Results are presented of Stromgren uvby(beta) photometry for 213 starsearlier than G0 and brigher than mpg of about 10.7 m inSelected Area 203. The observed area lies close to the geometric centerof the Chamaeleon-Musca dark clouds complex. The results yield V, (b-y),m1, c1, and beta on the standard systems, withoverall rms errors for one observation of one star of 0.010, 0.004,0.007, 0.009, and 0.011, respectively.
| UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
| UBV(RI)c photometry of some standard sequences in the Harvard F regions and in the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988MNRAS.231.1047M&db_key=AST
| Standard Stars for VRI Photometry with S25 Response Photocathodes
Not Available
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| Takýmyýldýz: | Bukalemun |
| Sað Açýklýk: | 12h13m54.16s |
| Yükselim: | -76°01'19.1" |
| Görünürdeki Parlaklýk: | 8.712 |
| Uzaklýk: | 208.333 parsek |
| özdevim Sað Açýklýk: | -54.2 |
| özdevim Yükselim: | -4.4 |
| B-T magnitude: | 9.326 |
| V-T magnitude: | 8.763 |
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