Using the Hubble Space Telescope (HST) and the Large Binocular Telescope, we followed the evolution of the Type Ia supernova (SN Ia) 2011fe for an unprecedented 1840 days past B-band maximum light and over a factor of 7 million in flux. At 1840 days, the 4000-17000{AA} quasi-bolometric luminosity is just (420+/-20)L_{sun}_. By measuring the late-time quasi-bolometric light curve, we present the first confident detection of ^57^Co decay in a SN Ia light curve and estimate a mass ratio of log(^57^Co/^56^Co)=-1.59_-0.07_^+0.06^. We do not have a clean detection of ^55^Fe, but find a limit of ^55^Fe/^57^Co<0.22 with 99% confidence. These abundance ratios provide unique constraints on the progenitor system because the central density of the exploding white dwarf(s) dictates these nucleosynthetic yields. The observed ratios strongly prefer the lower central densities of double-degenerate models (^55^Fe/^57^Co=0.27) over the higher central densities of near-Chandrasekhar-mass single-degenerate models (^55^Fe/^57^Co=0.68). However, additional theoretical studies predicting isotopic yields from a broader range of progenitor systems are motivated by these unique observations. We will continue to observe SN 2011fe for another ~600 days with HST and possibly beyond.
Photoelectric (UBVR) observations in 1998-2001 and medium-resolution spectroscopy obtained in the SAO in the same period for the B[e]/X-ray transient CI Cam display cyclic variations with a period of 1100 days.
We present results from a continuing campaign to secure deep multi-colour CCD sequences for photoelectric calibration in UK Schmidt fields with galactic latitudes |b|>50{deg}. In this paper, we present UBVR photometry in 12 fields and BR photometry in a further 14 fields observed within UK Schmidt survey fields centered at {delta}=-30{deg}. Our observations were carried out with the 0.9m Telecope at the Cerro-Tololo Inter-American Observatory.
We present photometry and a preliminary interpretation of a UBVR survey of the Large and Small Magellanic Clouds, which covers 14.5 deg^2^ and 7.2deg^2^, respectively. This study is aimed at obtaining well-calibrated data on the brighter, massive stars, complementing recent, deeper CCD surveys. Our catalog contains 179,655 LMC and 84,995 SMC stars brighter than V~18.0, and is photometrically complete to U~B~V~15.7 and R~15.2, although stars in crowded regions are selectively missed. We compare our photometry to that of others, and describe the need for gravity-dependent corrections to our CCD U-band photometry. We provide a preliminary cross-reference between our catalog stars and the stars with existing spectroscopy.
We present precision CCD light curves, a period study, photometrically derived standard magnitudes, and a five-color simultaneous Wilson code solution of the totally eclipsing, yet shallow amplitude (Av~0.4mag) eclipsing, binary V1853 Orionis. It is determined to be an extreme mass ratio, q=0.20, W-type W UMa overcontact binary. From our standard star observations, we find that the variable is a late-type F spectral-type dwarf, with a secondary component of about 0.24 solar masses (stellar type M5V). Its long eclipse duration (41 minutes) as compared to its period, 0.383-days, attests to the small relative size of the secondary. Furthermore, it has reached a Roche lobe fill-out of ~50% of its outer critical lobe as it approaches its final stages of binary star evolution, that of a fast spinning single star. Finally, a summary of about 25 extreme mass ratio solar-type binaries is given.
We present homogeneous, standardized UBV(RI)C photometry for over 700 nearby stars selected on the basis of Hipparcos parallaxes. Additionally, we list JHK photometry for about half of these stars, as well as L photometry for 86 of the brightest. A number of stars with peculiar colours or anomalous locations in various colour-magnitude diagrams are discussed.
We present UBVRcIc magnitudes of 49 comparison stars in the fields of the Seyfert galaxies Mrk 335, Mrk 79, Mrk 279, Mrk 506, 3C 382, 3C 390.3, NGC 6814, Mrk 304, Ark 564, and NGC 7469 in order to facilitate the photometric monitoring of these objects; 36 of the stars have not been calibrated before. The comparison stars are situated in 5x5arcmin fields centred on the Seyfert galaxies, their V band flux ranges from 11.7 to 18.2mag with a median value of 16.3mag, and their B-V colour index ranges from 0.4 to 1.6mag with a median value of 0.8mag. The median errors of the calibrated UBVRCIC magnitudes are 0.08, 0.04, 0.03, 0.04, and 0.06mag, respectively. Comparison stars were calibrated for the first time in three of the fields (Mrk 506, 3C 382, and Mrk 304). The comparison sequences in the other fields were improved in various aspects. Extra stars were calibrated in four fields (Mrk 335, Mrk 79, NGC 6814, and NGC 7469) most of these stars are fainter and are situated closer to the Seyfert galaxies compared to the existing comparison stars. The passband coverage of the sequences in five fields (Mrk 335, Mrk 79, Mrk 279, NGC 6814, and Ark 564) was complemented with the U band.
We report broadband UBV and/or BVR_C_I_C_ CCD photometry for a total of 1857 stars in the thick-disk and halo populations of the Galaxy. The majority of our targets were selected as candidate field horizontal-branch or other A-type stars (FHB/A, N=576), or candidate low-metallicity stars (N=1221), from the HK and Hamburg/ESO objective-prism surveys. Similar data for a small number of additional stars from other samples are also reported.
We have compared the results of multicolor UBVR and H{alpha} photometry for 169 young star-formation complexes in five galaxies using a grid of evolutionary models for young star clusters. The ages and interstellar absorptions are estimated for 102 star-formation complexes with the standard uncertainties {sigma}_t_=0.30dex and {sigma}_AV_=0.45mag. The accuracies of these parameters were verified using numerical simulations.
New UBVRI and H{alpha} photometry has been obtained for the young open cluster NGC 6530 located 10' east of the Lagoon Nebula (M8). We found 37 pre-main-sequence (PMS) stars with H{alpha} emission and nine PMS candidates using the R-H{alpha} color, a measure of H{alpha} emission. From this new photometry we derived the cluster parameters (V_0_-M_V_=11.25+/-0.1mag and E(B-V)=0.35mag), typical age (1.5Myr), and an age spread of about 5Myr. We confirmed the presence of a small amount of differential reddening across the cluster. We also verified the abnormal reddening law for the cluster, especially for a heavily embedded O7 V star, Herschel 36. Comparisons were made for several PMS evolution models with regard to the resulting age distribution and the initial mass function.
