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RR Lyrae Stars as a Tool to Measure Interstellar Reddening

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. Et al…. Brad Boswell Katie Guldenschuh Jeff Gregorsok Neil Beery Ciyeah Wan (MS) Alicia Day Nathan Walters

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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.

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