1,104 research outputs found
The ACS LCID Project: Variable Stars in Tucana and LGS3
We present preliminary results concerning the search for short-period
variable stars in Tucana and LGS3 based on very deep HST/ACS imaging. In the
one chip per galaxy we studied so far, a total of 230 and 80 candidates
variables were found, respectively. For Tucana, we identified 134 of them as RR
Lyrae stars (RRL) pulsating in the fundamental mode (RRab), 51 in the
first-overtone mode (RRc), and 37 in both modes simultaneoulsy (RRd), as well
as four candidate anomalous Cepheids (AC). In the case of LGS3, we found 45
RRab and 5 RRc, plus three candidates RRd and five candidate AC. The
metallicities obtained from the mean period of the RRab are [Fe/H]_{Tuc}=-1.7
and [Fe/H]_{LGS3}=-1.8.Comment: 2 pages, 1 figure. To appear in the Proceedings of IAU Symposium 241:
"Stellar Populations as Building Blocks of Galaxies", 10-16 December, 2006 at
La Palma, Canary Islands, Spai
Galactic Calibration of the Tip of the Red Giant Branch
Indications from Gaia data release 2 (DR2) are that the tip of the red giant
branch (TRGB, a population II standard candle related to the helium flash in
low mass stars) is close to -4 in absolute I magnitude in the Cousins
photometric system. Our sample is high latitude southern stars from the thick
disk and inner halo, and our result is consistent with longstanding findings
from globular clusters, whose distances were calibrated with RR Lyrae stars. As
the Gaia mission proceeds, there is every reason to think an accurate Galactic
geometric calibration of TRGB will be a significant outcome.Comment: to appear in PAS
Variable stars in the dwarf irregular galaxy NGC 6822: the photometric catalogue
Deep B,V time-series photometry obtained with the ESO Very Large Telescope
has been used to identify variable stars in the dwarf irregular galaxy NGC
6822. We surveyed a 6.8x6.8 arcmin area of the galaxy and detected a total
number of 390 candidate variables with the optimal image subtraction technique
(Alard 2000). Light curves on a magnitude scale were obtained for 262 of these
variables. Differential flux light curves are available for the remaining
sample. In this paper we present the photometric catalogue of calibrated light
curves and time-series data, along with coordinates and classification of the
candidate variables. A detailed description is provided of the procedures used
to identify the variable stars and calibrate their differential flux light
curves on a magnitude scale.Comment: 22 pages, 19 figures only as JPEG. Revised version with corrected eq.
5. Full text with better resolution .ps figures available upon request from
the authors. Uses aa.cls (included), in press on A&A. Table 2 will only be
published at the CDS, Appendix A, Tables 4,5,6 will only be available in the
electronic edition of the Journa
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