RR Lyrae Stars as a Tool to Measure Interstellar Reddening - PowerPoint PPT Presentation

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RR Lyrae Stars as a Tool to Measure Interstellar Reddening

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  1. RR Lyrae Stars as a Tool to Measure Interstellar Reddening Andrew Layden, Brad Boswell, et al. Bowling Green State University Variable Stars 2004, BGSU, April 3

  2. Et al… • Brad Boswell • Katie Guldenschuh • Jeff Gregorsok • Neil Beery • Ciyeah Wan (MS) • Alicia Day • Nathan Walters • Boncho Bonev (MS) • Nick Pearson

  3. Outline • Motivation for Project • Existing Data • New Data: Techniques & Examples • Analysis • Conclusions

  4. Motivation • RR Lyrae are Pop II standard candles. • Interstellar reddening affects distances: m-M = 5 log d - 5 + Av • Reddening maps iffy near Galactic Plane. • RRL have common color at min light.

  5. Existing Data • (a) B-V: • Sturch (1966) • Blanco (1992) • (b) V-I: • Mateo et al (1995) • Better in high reddening sites. • Less sensitive to metallicity? • Need more stars!

  6. New (V-I)0 Calibration • Select RRL from Fernley et al. (1998): • Span wide range in [Fe/H] and Period. • |b| > 20° from Galactic plane. • Reddening from Schlegel et al. (1998) map. • V and I images from BGSU 0.5-m + CCD: • Differential photom wrt 6-12 comp stars, • Typically 50-100 images per filter per star. • Comp star all-sky photom at WIYN 0.9-m.

  7. (a) [Fe/H] = -0.07 (b) [Fe/H] = -0.69

  8. (c) [Fe/H] = -1.63 (d) [Fe/H] = -1.95

  9. Analysis • Compute mean (V-I) over 0.5 < f < 0.8. • Subtract E(V-I) from Schlegel map. • Plot (V-I)0 vs [Fe/H] • Added 14 RRL. • Bluer than literature by ~0.03 mag… ? • <(V-I)0> = 0.57±0.01 (s = 0.02) mag.

  10. Conclusions • Calibrating <(V-I)0> for RRL: • 0.568 ± 0.004 (rand) ± 0.02 (syst), s = 0.023 mag • Weak [Fe/H] dependence: -0.015 mag/dex, • Simple and precise reddening indicator. • Coming this summer: • Add results from ~20 more field RRL, • Include RRL in globulars: period dependence, • Examine systematic shift wrt literature.

  11. References • Blanco 1992, AJ, 104, 734 • Cacciari et al. 1987, A&AS, 69, 135 • Clementini. et al. 1990, A&AS, 85, 865 • Fernley et al. 1998, MNRAS, 330, 515 • Liu & Janes 1989, ApJS, 69, 593 • Mateo et al. 1995, AJ, 109, 588 • Schlegel, Davis & Finkbiner 1998, ApJ, 500, 525 • Sturch 1966, ApJ, 143, 774 • Project funded by NSF, grant AST 99-88259.