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Title: The M33 Synoptic Stellar Survey. II. Mira Variables

Abstract

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 ∼2.4 × 10{sup 5} I -band light curves previously obtained by the M33 Synoptic Stellar Survey. We derive preliminary period–luminosity relations at optical, near-infrared, and mid-infrared wavelengths and compare them to the corresponding relations in the Large Magellanic Cloud.

Authors:
;  [1]; ; ;  [2]
  1. George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843 (United States)
  2. Department of Statistics, Texas A and M University, College Station, TX 77843 (United States)
Publication Date:
OSTI Identifier:
22663707
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 153; Journal Issue: 4; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ALGORITHMS; COMPARATIVE EVALUATIONS; DIAGRAMS; INTERMEDIATE INFRARED RADIATION; LUMINOSITY; MAGELLANIC CLOUDS; NEAR INFRARED RADIATION; RANDOMNESS; VARIABLE STARS; VISIBLE RADIATION; WAVELENGTHS

Citation Formats

Yuan, Wenlong, Macri, Lucas M., He, Shiyuan, Long, James, and Huang, Jianhua Z., E-mail: lmacri@tamu.edu. The M33 Synoptic Stellar Survey. II. Mira Variables. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA63F1.
Yuan, Wenlong, Macri, Lucas M., He, Shiyuan, Long, James, & Huang, Jianhua Z., E-mail: lmacri@tamu.edu. The M33 Synoptic Stellar Survey. II. Mira Variables. United States. doi:10.3847/1538-3881/AA63F1.
Yuan, Wenlong, Macri, Lucas M., He, Shiyuan, Long, James, and Huang, Jianhua Z., E-mail: lmacri@tamu.edu. Sat . "The M33 Synoptic Stellar Survey. II. Mira Variables". United States. doi:10.3847/1538-3881/AA63F1.
@article{osti_22663707,
title = {The M33 Synoptic Stellar Survey. II. Mira Variables},
author = {Yuan, Wenlong and Macri, Lucas M. and He, Shiyuan and Long, James and Huang, Jianhua Z., E-mail: lmacri@tamu.edu},
abstractNote = {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 ∼2.4 × 10{sup 5} I -band light curves previously obtained by the M33 Synoptic Stellar Survey. We derive preliminary period–luminosity relations at optical, near-infrared, and mid-infrared wavelengths and compare them to the corresponding relations in the Large Magellanic Cloud.},
doi = {10.3847/1538-3881/AA63F1},
journal = {Astronomical Journal (Online)},
number = 4,
volume = 153,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}
  • We have conducted a ground-based BVI synoptic survey of the Local Group galaxy M 33 which covers most of its disk and spans a period of 7 years. The survey targets luminous, long-period variables such as Cepheids and Miras and combines images from the DIRECT project and follow-up observations at the WIYN 3.5 m telescope. This paper, the first in a series, presents the discovery and characterization of 564 Cepheid variables, which represent a factor of two increase over previous samples with calibrated point-spread function (PSF) photometry. We also describe the details of the observations and analysis of the surveymore » data, including the use of archival Hubble Space Telescope images to characterize biases in our ground-based PSF photometry.« less
  • High-resolution (..delta..sigmaapprox. =0.15 cm/sup -1/) infrared spectra in the 4000--6700 cm/sup -1/ region of the bright Mira variable R Leonis have been searched for stellar water bands. Three bands are readily identified in the spectra, two in the 5300 cm/sup -1/ (1.9..mu..m) region and another in the 6700 cm/sup -1/ (1.5..mu..m) region. Two bands may also be present in the very blended 4000 cm/sup -1/ region (2.5..mu..m). The radial velocities, central depths, and equivalent widths of the lines in the 1.9..mu..m bands were measured.At phases other than maximum light, two separate layers of the atmosphere contribute to the H/sub 2/Omore » spectrum. On the basis of radial velocity, excitation temperature, and broadening of the lines, these two layers are identified with the two CO and OH line-forming regions described by Hinkle (1978a). The water spectrum originates near the boundary layers of the photosphere at T/sub exc/(H/sub 2/O) approx. = 1700 K, and in a cooler, overlying region with T/sub exc/(H/sub 2/O) approx. =1100 K. At maximum light only the 1100 K region contributes H/sub 2/O lines. The photospheric H/sub 2/O radial velocity curve is compared with the photospheric CO and OH curves, and further evidence is presented for a pulsation-shock model for Mira variables. The details of the 1100 K region velocity curve and equivalent widths are also discussed.Using a curve of growth for a plane-parallel isothermal layer, an approximate column density of 5 x 10/sup 21/ H/sub 2/O molecules cm/sup -2/ through the entire atmosphere of R Leo is derived. Phase-dependent variations in the column density of an order of magnitude occur during the light cycle. Pervious analyses of H/sub 2/O in Mira variables, including those using the 201--000 band at 9400 A, are reviewed.« less
  • An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors and their evolutionary state. A greatly improved census of the likely progenitor class, including the most luminous evolved stars, the luminous blue variables (LBVs), and the warm and cool hypergiants is now needed for a complete picture of the final pre-supernova stages of very massive stars. We have begun a survey of the evolved and unstable luminous star populations in several nearby resolved galaxies. In this second paper on M31 and M33, we reviewmore » the spectral characteristics, spectral energy distributions, circumstellar ejecta, and evidence for mass loss for 82 luminous and variable stars. We show that many of these stars have warm circumstellar dust including several of the Fe II emission line stars, but conclude that the confirmed LBVs in M31 and M33 do not. The confirmed LBVs have relatively low wind speeds even in their hot, quiescent or visual minimum state compared to the B-type supergiants and Of/WN stars which they spectroscopically resemble. The nature of the Fe II emission line stars and their relation to the LBV state remains uncertain, but some have properties in common with the warm hypergiants and the sgB[e] stars. Several individual stars are discussed in detail. We identify three possible candidate LBVs and three additional post-red supergiant candidates. We suggest that M33-013406.63 (UIT301,B416) is not an LBV/S Dor variable, but is a very luminous late O-type supergiant and one of the most luminous stars or pair of stars in M33.« less
  • We present the results of an extensive survey of RR Lyrae (RRL) stars in three fields along the major axis of the Triangulum Galaxy (M33). From images taken with the Advanced Camera for Surveys (ACS) Wide Field Channel on board the Hubble Space Telescope through two passbands (F606W and F814W), we have identified and characterized a total of 119 RRL variables (96 RRab (RR0) and 23 RRc (RR1)) in M33. Using the properties of 83 RRL stars (65 RRab and 18 RRc) in the innermost ACS field (hereafter DISK2), we find mean periods of (P{sub ab}) = 0.553 {+-} 0.008more » (error1) {+-} 0.05 (error2) and (P{sub c}) = 0.325 {+-} 0.008 (error1) {+-} 0.05 (error2), where the 'error1' value represents the standard error of the mean and the 'error2' value is based on the error of an individual RRL period calculated from our synthetic light curve simulations. The distribution of RRab periods and the frequency of RRc stars (N{sub c} = n{sub c} /n{sub abc} = 0.22) strongly suggest that these RRLs follow the general characteristics of those in Oosterhoff type I Galactic globular clusters. The metallicities of 65 individual RRab stars are calculated from the period-amplitude-metallicity relationship, yielding a mean metallicity of ([Fe/H]) = -1.48 {+-} 0.05 dex, where the uncertainty is the standard error of the mean. The VI minimum-light colors of the RRab stars are used to calculate a mean line-of-sight reddening toward the DISK2 field of (E(V - I)) = 0.175. By adopting this line-of-sight reddening and using a relation between RRL luminosity and metallicity (M{sub V} = 0.23[Fe/H]+0.93), we estimate a mean distance modulus of ((m - M){sub 0}) = 24.52 {+-} 0.11 for M33, where the error is the quadratic sum of the uncertainties in the absolute and dereddened V magnitudes of the RRLs. The Oosterhoff I properties of the M33 field RRL stars agree well with those of RRL populations found in the M31 halo consistent with the past interaction history of these two galaxies.« less