211 research outputs found
Cepheid Variables in the Maser-Host Galaxy NGC 4258
We present results of a ground-based survey for Cepheid variables in NGC
4258. This galaxy plays a key role in the Extragalactic Distance Scale due to
its very precise and accurate distance determination via VLBI observations of
water masers. We imaged two fields within this galaxy using the Gemini North
telescope and GMOS, obtaining 16 epochs of data in the SDSS gri bands over 4
years. We carried out PSF photometry and detected 94 Cepheids with periods
between 7 and 127 days, as well as an additional 215 variables which may be
Cepheids or Population II pulsators. We used the Cepheid sample to test the
absolute calibration of theoretical gri Period-Luminosity relations and found
good agreement with the maser distance to this galaxy. The expected data
products from the Large Synoptic Survey Telescope (LSST) should enable Cepheid
searches out to at least 10 Mpc.Comment: Accepted for publication in the Astronomical Journa
Blending of Cepheids in M33
A precise and accurate determination of the Hubble constant based on Cepheid
variables requires proper characterization of many sources of systematic error.
One of these is stellar blending, which biases the measured fluxes of Cepheids
and the resulting distance estimates. We study the blending of 149 Cepheid
variables in M33 by matching archival Hubble Space Telescope data with images
obtained at the WIYN 3.5-m telescope, which differ by a factor of 10 in angular
resolution.
We find that 55+-4% of the Cepheids have no detectable nearby companions that
could bias the WIYN V-band photometry, while the fraction of Cepheids affected
below the 10% level is 73+-4%. The corresponding values for the I band are
60+-4% and 72+-4%, respectively. We find no statistically significant
difference in blending statistics as a function of period or surface
brightness. Additionally, we report all the detected companions within 2
arcseconds of the Cepheids (equivalent to 9 pc at the distance of M33) which
may be used to derive empirical blending corrections for Cepheids at larger
distances.Comment: v2: Fixed incorrect description of Figure 2 in text. Accepted for
publication in AJ. Full data tables can be found in ASCII format as part of
the source distribution. A version of the paper with higher-resolution
figures can be found at
http://faculty.physics.tamu.edu/lmacri/papers/chavez12.pd
The M33 Synoptic Stellar Survey. II. Mira Variables
We present the discovery of 1847 Mira candidates in the Local Group galaxy
M33 using a novel semi-parametric periodogram technique coupled with a Random
Forest classifier. The algorithms were applied to ~2.4x10^5 I-band light curves
previously obtained by the M33 Synoptic Stellar Survey. We derive preliminary
Period-Luminosity relations at optical, near- & mid-infrared wavelengths and
compare them to the corresponding relations in the Large Magellanic Cloud.Comment: Includes small corrections to match the published versio
Variability of Young Massive Stars in the Arches Cluster
We present preliminary results of the first near-infrared variability study
of the Arches cluster, using adaptive optics data from NIRI/Gemini and
NACO/VLT. The goal is to discover eclipsing binaries in this young (2.5 +- 0.5
Myr), dense, massive cluster for which we will determine accurate fundamental
parameters with subsequent spectroscopy. Given that the Arches cluster contains
more than 200 Wolf-Rayet and O-type stars, it provides a rare opportunity to
determine parameters for some of the most massive stars in the Galaxy.Comment: 2 pages, to appear in the proceedings of the IAUS 272 on "Active OB
stars: structure, evolution, mass loss and critical limits" (Paris, July
19-23, 2010), Cambridge University Press. Editors C. Neiner, G. Wade, G.
Meynet and G. Peter
On the Variation of Fourier Parameters for Galactic and LMC Cepheids at Optical, Near-Infrared and Mid-Infrared Wavelengths
We present a light curve analysis of fundamental-mode Galactic and Large
Magellanic Cloud (LMC) Cepheids based on the Fourier decomposition technique.
We have compiled light curve data for Galactic and LMC Cepheids in optical
({\it VI}), near-infrared ({\it JHK}) and mid-infrared (3.6
4.5-m) bands from the literature and determined the variation of their
Fourier parameters as a function of period and wavelength. We observed a
decrease in Fourier amplitude parameters and an increase in Fourier phase
parameters with increasing wavelengths at a given period. We also found a
decrease in the skewness and acuteness parameters as a function of wavelength
at a fixed period. We applied a binning method to analyze the progression of
the mean Fourier parameters with period and wavelength. We found that for
periods longer than about 20 days, the values of the Fourier amplitude
parameters increase sharply for shorter wavelengths as compared to wavelengths
longer than the -band. We observed the variation of the Hertzsprung
progression with wavelength. The central period of the Hertzsprung progression
was found to increase with wavelength in the case of the Fourier amplitude
parameters and decrease with increasing wavelength in the case of phase
parameters. We also observed a small variation of the central period of the
progression between the Galaxy and LMC, presumably related to metallicity
effects. These results will provide useful constraints for stellar pulsation
codes that incorporate stellar atmosphere models to produce Cepheid light
curves in various bands.Comment: 22 pages, 19 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Society Main Journa
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