Anna Katherina Vivas

The QUEST RR Lyrae Survey: Confirmation of the Clump at 50 Kiloparsecs and Other Overdensities in the Outer Halo

We have measured the periods and light curves of 148 RR Lyrae variables from V = 13.5 to 19.7 from the first 100 deg2 of the Quasar Equatorial Survey Team RR Lyrae survey. Approximately 55% of these stars belong to the clump of stars detected earlier by the Sloan Digital Sky Survey. According to our measurements, this feature has ~10 times the background density of halo stars, spans at least 375 by 35 in α and δ (≥30 by ≥3 kpc), lies ~50 kpc from the Sun, and has a depth along the line of sight of ~5 kpc (1 σ). These properties are consistent with the recent models that suggest that it is a tidal stream from the Sagittarius dwarf spheroidal galaxy. The mean period of the type ab variables, 0.58 days, is also consistent. In addition, we have found two smaller overdensities in the halo, one of which may be related to the globular cluster Pal 5.

Reddening-independent quasar selection from a wide-field optical and near-infrared imaging survey

We combine deep, wide-eld near-IR and optical imaging to de monstrate a reddening- independent quasar selection technique based on identifying outliers in the (g z) / (z H) colour diagram. In three elds covering a total of IR excesses. 2 of 8 quasars from a subsample with U band observations do not exhibit UVX colours. From these preliminary results, we suggest that this combined optical and near-IR selection technique has a high selection ecien cy (> 65% success rate), a high surface density of candidates, and is relatively independent of reddening. We discuss the implications for star/galaxy separation for IR base surveys for quasars. We provide the coordinate list and follow-up spectroscopy for the sample of 22 conrmed quasars.

A Large‐Area CCD Camera for the Schmidt Telescope at the Venezuelan National Astronomical Observatory

We have designed, constructed, and put into operation a large-area CCD camera that covers a large fraction of the image plane of the 1 m Schmidt telescope at Llano del Hato in Venezuela. The camera consists of 16 CCD devices arranged in a 4 × 4 mosaic covering 23 × 35 of sky. The CCDs are 2048 × 2048 LORAL devices with 15 μm pixels. The camera is optimized for drift-scan photometry and objective-prism spectroscopy. The design considerations, construction features, and performance parameters are described in the following paper.

The low-mass star and sub-stellar populations of the 25 Orionis group

We present the results of a survey of the low mass star and brown dwarf population of the 25 Orionis group. Using optical photometry from the CIDA Deep Survey of Orion, near IR photometry from the Visible and Infrared Survey Telescope for Astronomy and low resolution spectroscopy obtained with Hectospec at the MMT, we selected 1246 photometric candidates to low mass stars and brown dwarfs with estimated masses within 0.02 <M/M⊙ <0.8 and spectroscopically confirmed a sample of 77 low mass stars as new members of the cluster with a mean age of �7 Myr. We have obtained a system initial mass function of the group that can be well described by either a Kroupa power-law function with indices α3 = 1.73 ± 0.31 and α2 = 0.68 ± 0.41 in the mass ranges 0.03 6 M/M⊙ 6 0.08 and 0.08 6 M/M⊙ 6 0.5 respectively, or a Scalo log-normal function with coefficientsmc = 0.21 +0.02 −0.02 and σ = 0.36 ± 0.03 in the mass range 0.03 6 M/M⊙ 6 0.8. From the analysis of the spatial distribution of this numerous candidate sample, we have confirmed the EastWest elongation of the 25 Orionis group observed in previous works, and rule out a possible southern extension of the group. We find that the spatial distributions of low mass stars and brown dwarfs in 25 Orionis are statistically indistinguishable. Finally, we found that the fraction of brown dwarfs showing IR excesses is higher than for low mass stars, supporting the scenario in which the evolution of circumstellar discs around the least massive objects could be more prolonged.