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RR Lyrae Stars: A Look at Variability in the SDSS-II Supernova Survey

July 24 2007. Cycles of Discovery and Stellar Pulsation. Outline. A Quick Look at Bailey TypesThe Sloan Digital Sky SurveyCandidate RR LyraeGalactic HaloMetallicity DeterminationRRL SpectroscopyFuture Work. July 24 2007. Cycles of Discovery and Stellar Pulsation. Bailey Types. Based on light c

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RR Lyrae Stars: A Look at Variability in the SDSS-II Supernova Survey

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    1. RR Lyrae Stars: A Look at Variability in the SDSS-II Supernova Survey Nathan De Lee (Michigan State) H. A. Smith, T. C. Beers (MSU) D. M. Bramich, S. Vidrih, and D. B. Zucker (IoA, Cambridge) . Ivezic (Univ. of Washington)

    2. July 24 2007 Cycles of Discovery and Stellar Pulsation Outline A Quick Look at Bailey Types The Sloan Digital Sky Survey Candidate RR Lyrae Galactic Halo Metallicity Determination RRL Spectroscopy Future Work

    3. July 24 2007 Cycles of Discovery and Stellar Pulsation Bailey Types Based on light curve shape RRab Fundamental Mode RRc First Overtone

    4. July 24 2007 Cycles of Discovery and Stellar Pulsation Sloan Digital Sky Survey The Sloan Digital Sky Survey (SDSS) is the largest photometric / spectroscopic survey to date. Uses Apache Point 2.5 meter telescope. As of Data Release 6: Imaging: 9583 sq. deg Spectra: 6860 sq. deg 287 x106 unique objects 1,271,680 spectra taken

    5. July 24 2007 Cycles of Discovery and Stellar Pulsation The ugriz Filter System The ugriz filter system is defined on the 2.5m survey telescope. This system will be used on upcoming missions (Pan-STARRS etc). The ugriz filter system is fundamentally different than the Johnson-Cousins UBVRI system. Currently, there is very little data on RRL in the ugriz system.

    6. July 24 2007 Cycles of Discovery and Stellar Pulsation SDSS SN Survey The SDSS-II Supernova Survey covers a 300 sq degree field. Stripe 82 covers: 20h < RA < 4h -1.25 < DEC < 1.25 The survey imaged this region with a 2-day cadence over a 3 month period in both 2005 and 2006 and is scheduled to do it again in 2007.

    7. July 24 2007 Cycles of Discovery and Stellar Pulsation SN Survey Location The SN Survey covers a region of high southern Galactic latitudes primarily in the anti-center direction. It is a good complement for previous surveys, in particular the QUEST survey.

    8. July 24 2007 Cycles of Discovery and Stellar Pulsation Other Surveys There have been several unfiltered variable star surveys including most recently the LONEOS-I Survey and the Northern Sky Variability Survey (NSVS) (Kinemuchi et al. 2006)

    9. July 24 2007 Cycles of Discovery and Stellar Pulsation Light-Motion-Curve Catalogue The photometry used in this RRL search came from Version 1 of the Light-Motion-Curve Catalogue (LMCC) (Bramich 2007). This catalog covers approximately 250 sq degrees and includes data from 1998 through 2005 (including the SN Survey). There is also a Higher-Level Catalogue (HLC) which provides derived properties of the stars including position, colors, reddening, etc.

    10. July 24 2007 Cycles of Discovery and Stellar Pulsation RR Lyrae Selection Criteria Welch-Stetson variability index >= 2 Maximum magnitude g0 <= 21.5 Number of good epochs >= 5 in g,r,i Color cuts as described in Ivezic et al. (2005). This resulted in 293 RRL with 191 RRab 102 RRc.

    11. July 24 2007 Cycles of Discovery and Stellar Pulsation

    12. July 24 2007 Cycles of Discovery and Stellar Pulsation

    13. July 24 2007 Cycles of Discovery and Stellar Pulsation Spatial Distribution One can see that the spatial distribution for the RRL is the similar to a random subset of stars. There does seem to be a bump around RA of 380 that we intend to investigate more.

    14. July 24 2007 Cycles of Discovery and Stellar Pulsation Period-Amplitude Diagram The Oosterhoff type I and II lines were converted from Clement & Rowe (2000) using Ag/AV = 1.17 The majority of the RRab stars fall along the OOI as seen in previous studies of the field.

    15. July 24 2007 Cycles of Discovery and Stellar Pulsation Galactic Halo Recent studies have strongly suggested that the Milky Way halo consists of two parts (Kinman et al. 2007) and (Miceli et al. 2007) : Inner Halo: Older, formed from dissipative collapse. Outer Halo: Younger, formed from accretion.

    16. July 24 2007 Cycles of Discovery and Stellar Pulsation RRL as Tracer Stars RRL are powerful tracer stars: Standard Candles Readily identifiable Lightcurve shape is related to metallicity. Period and RRab/RRc are indicative of different population types (Oosterhoff groups). Our sample of 293 RRL extends through the interface of the two halos (10-15 kpc) into the outer halo distance (6-75 kpc).

    17. July 24 2007 Cycles of Discovery and Stellar Pulsation Determining Metallicity: Fourier Coefficients The shape of a light curve can be described by a discrete Fourier series. In previous work, Ive used a sine series up to order 8. Work by Jurcsik & Kovacs (1996), Sandage (2004), and Morgan (2007) show an empirical relationship between metallicity and Fourier parameters.

    18. July 24 2007 Cycles of Discovery and Stellar Pulsation MSU 24inch Observatory The first step to determining the Fourier coefficient metallicity relation is observe well studied RRL in g, r, and i. The MSU observatory gives us the ability to do this, barring issues with the weather.

    19. July 24 2007 Cycles of Discovery and Stellar Pulsation X Ari

    20. July 24 2007 Cycles of Discovery and Stellar Pulsation Determining Metallicity: SDSS RRL Spectra Spectroscopy is fundamental to determining space motions and metallicity. RRL stars are pulsating stars, so it is important to know what phase they are in when one takes spectra. The lines of this RRL change significantly with phase.

    21. July 24 2007 Cycles of Discovery and Stellar Pulsation SDSS Spectra We have medium-resolution SDSS spectra for approximately 120 RRL in our sample. Of those, approximately 70 have spectra taken at appropriate epochs to get useful metallicity and radial velocity information out.

    22. July 24 2007 Cycles of Discovery and Stellar Pulsation SEGUE/SDSS-II Pipeline As part of Data Release 6 there is now a pipeline for the automatic determination of stellar parameters from SDSS spectra (Lee et al. 2007). Heliocentric Radial velocity errors of 7 km/s This pipeline uses several methods to determine [Fe/H]. The metallicities from the spectra have errors on order of 0.2 dex.

    23. July 24 2007 Cycles of Discovery and Stellar Pulsation Template and Spline Fitting To determine epochs of maximum we use both template and spline fitting. The templates are taken from Layden (1998).

    24. July 24 2007 Cycles of Discovery and Stellar Pulsation Spectra

    25. July 24 2007 Cycles of Discovery and Stellar Pulsation Putting it all together By combining metallicities and radial velocities from spectra with lightcurves, periods, and proper motions from the LMCC/HLC catalog, we can create a set of very good tracer stars. One with complete space motion and metallicity information. We can also use these stars to calibrate the Fourier components methods to find metallicities for all stars in our survey. Finally, using these stars we can investigate the different components of the halo.

    26. July 24 2007 Cycles of Discovery and Stellar Pulsation Further Work Expand the number of RRL candidates in the SDSS-II sample by relaxing the color cuts. Incorporate 2006 data into the lightcurves for better shape and period information. Use the improved lightcurve information to do Fourier component analysis. Obtain medium-resolution spectra for some of our candidates on the Blanco 4m telescope.

    27. July 24 2007 Cycles of Discovery and Stellar Pulsation References Bramich et al. 2007, in preparation Clement, C. M., & Rowe, J. 2000, AJ, 120, 2579 Ivezic, ., Vivas, A. K., Lupton, R. H., & Zinn, R. 2005, AJ, 129, 1096 Jurcsik, J., & Kovacs, G. 1996, A&A, 312, 111 Kinemuchi, K., Smith, H.A., Wozniak, P.R., & McKay, T. A. 2006, AJ, 132, 1202 Kinman et al. 2007, MNRAS,375,1381 Layden, A.C. 1998, AJ, 115, 193 Lee et al. 2007, in preparation Miceli, A., et al. 2007, ArXiv e-prints, 706, arXiv:0706.1583 Morgan, S.M., Wahl, J.N., & Wieckhorst, R.M. 2007, MNRAS, 374, 1421 Sandage, A. 2004, AJ, 128, 858 Smith, H.A. 1984, PASP, 96, 505 Vivas, A.K., et al. 2004, AJ, 127, 1158

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