192 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
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
Erratum: "Groups of Galaxies in the Two Micron All Sky Redshift Survey" (ApJ, 655, 790 [2007])
Large Magellanic Cloud Near-Infrared Synoptic Survey. II. The Wesenheit relations and their application to the Distance scale
We present new near-infrared Cepheid Period-Wesenheit relations in the LMC
using time-series observations from the Large Magellanic Cloud Near-Infrared
Synoptic Survey. We also derive opticalnear-infrared P-W relations using
and ~magnitudes from OGLE-III. We employ our new data to determine
an independent distance to the LMC of ~mag, using an absolute calibration of the Galactic
relations based on several distance determination methods and accounting for
the intrinsic scatter of each technique. We also derive new near-infrared
Period-Luminosity and Wesenheit relations for Cepheids in M31 using
observations from the PHAT survey. We use the absolute calibrations of the
Galactic and LMC relations to determine the distance modulus of M31,
~mag. We apply a simultaneous fit to Cepheids in
several Local Group galaxies covering a range of metallicities
(~dex) to determine a global slope of
-~mag/dex for the relation and obtain robust
distance estimates. Our distances are in good agreement with recent TRGB based
distance estimates and we do not find any evidence for a metallicity dependence
in the near-infrared P-W relations.Comment: 16 pages, 8 figures, Accepted for publication in The Astronomical
Journa
Cepheids and Long Period Variables in M33
We are conducting a long-term photometric survey of the nearby galaxy M33 to
discover Cepheids, eclipsing binaries, and long-period variables. The dataset
combines previously-obtained optical images from the DIRECT project with new
observations acquired at the WIYN 3.5m telescope. The entire data set spans
over 7 years with excellent synoptic coverage which will enable the discovery
and characterization of stars displaying variability over a wide range of
timescales (days, weeks, months, years). In this preliminary work we show
representative light curves of different variables we found so far in two
fields, color-magnitude diagrams, and optical Cepheid Period-Luminosity
relations for M33. The ultimate goal of the project is to provide an absolute
calibration of the Cepheid Period-Luminosity relation, and to study its
metallicity dependence at optical wavelengths.Comment: 3 pages, 6 figures. To appear in "Stellar Pulsation: Challenges for
Theory and Observation", Eds. J. Guzik and P. Bradle
A First Look at Cepheids in a SN Ia Host with JWST
We report the first look at extragalactic Cepheid variables with the James
Webb Space Telescope, obtained from a serendipitous (to this purpose)
observation of NGC 1365, host of an SN Ia (SN 2012fr), a calibration path used
to measure the Hubble constant. As expected, the high-resolution observations
with NIRCam through F200W show better source separation from line-of-sight
companions than HST images at similar near-infrared wavelengths, the spectral
region that has been used to mitigate the impact of host dust on distance
measurements. Using the standard star P330E as a zeropoint and PSF reference,
we photometered 31 previously-known Cepheids in the JWST field, spanning 1.15 <
log P < 1.75 including 24 Cepheids in the longer period interval of 1.35 < log
P < 1.75. We compared the resultant Period-Luminosity relations to that of 49
Cepheids in the full period range including 38 in the longer period range
observed with WFC3/IR on HST and transformed to the JWST photometric system
(F200W, Vega). The P-L relations measured with the two space telescopes are in
good agreement, with intercepts (at log P=1) of 25.74+/-0.04 and 25.72+\-0.05
for HST and JWST, respectively. Our baseline result comes from the longer
period range where the Cepheids have higher signal-to-noise ratios where we
find 25.75+\-0.05 and 25.75+\-0.06 mag for HST and JWST, respectively. We find
good consistency between this first JWST measurement and HST, and no evidence
that HST Cepheid photometry is "biased bright" at the ~0.2 mag level that would
be needed to mitigate the Hubble Tension, though comparisons from more SN hosts
are warranted and anticipated. We expect future JWST observations to surpass
these in quality as they will be optimized for measuring Cepheids.Comment: 11 pages, 4 figure
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