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 Brad Boswell Katie Guldenschuh Katie Guldenschuh Jeff Gregorsok Jeff Gregorsok Neil Beery Neil Beery Ciyeah Wan (MS) Ciyeah Wan (MS) Alicia Day Alicia Day Nathan Walters Nathan Walters Boncho Bonev (MS) Boncho Bonev (MS) Nick Pearson Nick Pearson

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

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

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!

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

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

(c) [Fe/H] = (d) [Fe/H] = (c) [Fe/H] = (d) [Fe/H] =

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

Conclusions Calibrating for RRL: Calibrating for RRL: ± (rand) ± 0.02 (syst),  = mag ± (rand) ± 0.02 (syst),  = mag Weak [Fe/H] dependence: mag/dex, Weak [Fe/H] dependence: mag/dex, Simple and precise reddening indicator. Simple and precise reddening indicator. Coming this summer: Coming this summer: Add results from ~20 more field RRL, Add results from ~20 more field RRL, Include RRL in globulars: period dependence, Include RRL in globulars: period dependence, Examine systematic shift wrt literature. Examine systematic shift wrt literature.

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