The Swift/UVOT Stars Survey. II. RR Lyrae Stars in M 3 and M 15

Abstract

We present the first results of an near-ultraviolet (NUV) survey of RR Lyrae stars from the Ultraviolet Optical Telescope (UVOT) aboard the Swift Gamma-Ray Burst Mission. It is well-established that RR Lyrae have large amplitudes in the far- and near-ultraviolet. We have used UVOT's unique wide-field NUV imaging capability to perform the first systematic NUV survey of variable stars in the Galactic globular clusters M 3 and M 15. We identify 280 variable stars, comprising 275 RR Lyrae, two anomalous Cepheids, one classical Cepheid, one SX Phoenicis star and one possible long-period or irregular variable. Only two of these are new discoveries. We compare our results to previous investigations and find excellent agreement in the periods with significantly larger amplitudes in the NUV. We map out, for the first time, an NUV Bailey diagram from globular clusters, showing the usual loci for fundamental mode RRab and first overtone RRc pulsators. We show the unique sensitivity of NUV photometry to both the temperatures and the surface gravities of RR Lyrae stars. Finally, we show evidence of an NUV period-metallicity-luminosity relationship. Future investigations will further examine the dependence of NUV pulsation parameters on metallicity and Oosterhoff classification.

50 pages, 24 figures, accepted to AJ

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• The Dartmouth Stellar Evolution Database
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Cited by in corpus (12)

• Intensive disc-reverberation mapping of Fairall 9: 1st year of Swift & LCO monitoring
• High-precision distance measurements with classical pulsating stars
• Near-infrared Census of RR Lyrae variables in the Messier 3 globular cluster and the Period--Luminosity Relations
• Periods and classifications of RR Lyrae stars in the globular cluster M15
• Multi-wavelength Photometric Study of RR Lyrae Variables in the Globular Cluster NGC 5272 (Messier 3)
• Near-ultraviolet detections of four dwarf nova candidates in the globular cluster 47 Tucanae
• TUVOpipe: a pipeline to search for UV transients with Swift-UVOT
• Far-ultraviolet investigation into the galactic globular cluster M30 (NGC 7099): I. Photometry and radial distributions
• PIPS, an advanced platform for period detection in time series -- I. Fourier-likelihood periodogram and application to RR Lyrae Stars
• A search for photometric variability towards the globular cluster M3 with the TWenty Inch Survey Telescope
• The Stripped-Star Ultraviolet Magellanic Cloud Survey (SUMS): The UV Photometric Catalog and Stripped Star Candidate Selection
• Optical and near-infrared pulsation properties of RR Lyrae and Population II Cepheid variables in the Messier 15 globular cluster