603 research outputs found
A Double-Mode RR Lyrae Star with a Strong Fundamental Mode Component
NSVS 5222076, a thirteenth magnitude star in the Northern Sky Variability
Survey, was identified by Oaster as a possible new double-mode RR Lyrae star.
We confirm the double-mode nature of NSVS 5222076, supplementing the survey
data with new V band photometry. NSVS 5222076 has a fundamental mode period of
0.4940 day and a first overtone period of 0.3668 day. Its fundamental mode
light curve has an amplitude twice as large as that of the first overtone mode,
a ratio very rarely seen. Data from the literature are used to discuss the
location in the Petersen diagram of double-mode RR Lyrae stars having strong
fundamental mode pulsation. Such stars tend to occur toward the short period
end of the Petersen diagram, and NSVS 5222976 is no exception to this rule.Comment: 14 pages, 4 figures, To be published in the March, 2006, issue of
PAS
RR Lyrae Variables in M33. I. Evidence For a Field Halo Population
We present observations of RR Lyrae variables in the Local Group late-type
spiral galaxy M33. Using the Advanced Camera for Surveys on the Hubble Space
Telescope, we have identified 64 ab-type RR Lyraes in M33. We have estimated
reddenings for these stars based on their minimum light V-I colors and
metallicities based on their periods. From the distributions of these
properties, we conclude that the RR Lyraes belong to two populations - one
associated with the halo of M33 and the other with its disk. Given that RR
Lyraes are produced by populations older than ~10 Gyr, this suggests that not
only does the field halo of M33 contain an old component, but so does its disk.
This is one of the best pieces of evidence for the existence of a halo field
component in M33. Using a relation between RR Lyrae absolute magnitude and
metallicity (Mv(RR) = 0.23[Fe/H] + 0.93), we estimate a mean distance modulus
of = 24.67 +/- 0.08 for M33. This places M33 approximately 70 kpc
beyond M31 in line-of-sight distance.Comment: 20 pages, 17 figures, accepted for publication in The Astronomical
Journa
Analysis of RR Lyrae Stars in the Northern Sky Variability Survey
We use data from the Northern Sky Variability Survey (NSVS), obtained from
the first generation Robotic Optical Transient Search Experiment (ROTSE-I), to
identify and study RR Lyrae variable stars in the solar neighborhood. We
initially identified 1197 RRab (RR0) candidate stars brighter than the ROTSE
median magnitude V = 14. Periods, amplitudes, and mean V magnitudes are
determined for a subset of 1188 RRab stars with well defined light curves.
Metallicities are determined for 589 stars by the Fourier parameter method and
by the relationship between period, amplitude, and [Fe/H]. We comment upon the
difficulties of clearly classifying RRc (RR1) variables in the NSVS dataset.
Distances to the RRab stars are calculated using an adopted
luminosity-metallicity relation with corrections for interstellar extinction.
The 589 RRab stars in our final sample are used to study the properties of the
RRab population within 5 kpc of the Sun. The Bailey diagram of period versus
amplitude shows that the largest component of this sample belongs to Oosterhoff
type I. Metal-rich ([Fe/H] > -1) RRab stars appear to be associated with the
Galactic disk. Our metal-rich RRab sample may include a thin disk as well as a
thick disk population, although the uncertainties are too large to establish
this. There is some evidence among the metal-rich RRab stars for a decline in
scale height with increasing [Fe/H], as was found by Layden (1995). The
distribution of RRab stars with -1 < [Fe/H] < -1.25 indicates that within this
metallicity range the RRab stars are a mixture of stars belonging to halo and
disk populations.Comment: 68 pages, 26 figures, 9 tables, accepted to A
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