1. Variable Stars in NGC 6304 Nathan De Lee (MSU) Horace Smith (Advisor) (MSU) Barton Pritzl (Macalester College) Marcio Catelan (PUC) Allen Sweigart (GSFC)

2. De Lee April 2004Michigan State University Overview Basic Properties of RR Lyrae StarsBasic Properties of RR Lyrae Stars The Oosterhoff DichotomyThe Oosterhoff Dichotomy NGC 6388 and NGC 6441NGC 6388 and NGC 6441 Methods for AnalysisMethods for Analysis NGC 6304 ResultsNGC 6304 Results Where to Go From HereWhere to Go From Here

3. De Lee April 2004Michigan State University RR Lyrae Variables Population II stars (Age > 10 Gyr)Population II stars (Age > 10 Gyr) Horizontal Branch StarsHorizontal Branch Stars Radially PulsatingRadially Pulsating Standard Candles M V .6Standard Candles M V .6 (Smith 1995)

4. De Lee April 2004Michigan State University Bailey Types Based on light curve shapeBased on light curve shape RRab Fundamental ModeRRab Fundamental Mode RRc First OvertoneRRc First Overtone

5. De Lee April 2004Michigan State University The Oosterhoff Dichotomy In 1939, Oosterhoff noticed a division in GC RR stars.In 1939, Oosterhoff noticed a division in GC RR stars. OOI OOII OOI OOII.55 d.64 d.55 d.64 d.32 d.37 d.32 d.37 d N RRc /N total.17.44 (Oosterhoff 1939)

6. De Lee April 2004Michigan State University Other Properties The Oosterhoff types are also metallicity groups.The Oosterhoff types are also metallicity groups. Oosterhoff type I have [Fe/H] > -1.7Oosterhoff type I have [Fe/H] > -1.7 Oosterhoff type II have [Fe/H] < -1.7Oosterhoff type II have [Fe/H] < -1.7

7. De Lee April 2004Michigan State University [Fe/H] Dichotomy (Smith 1995)

8. De Lee April 2004Michigan State University Do we fully understand the Oosterhoff Groups? There are a several issues that have appeared in the story of the Oosterhoff groups. There are a several issues that have appeared in the story of the Oosterhoff groups. First, the Oosterhoff dichotomy may be particular to the Milky Way. First, the Oosterhoff dichotomy may be particular to the Milky Way.

9. De Lee April 2004Michigan State University Milky Way GC The Oosterhoff gap in this version of the Period Metallicity Graph is filled with GCs from the LMC. (Catelan & Prizl 2004)

10. De Lee April 2004Michigan State University Other Issues In general, metal rich GCs should have a stubby red clump that doesn’t cross the instability strip.In general, metal rich GCs should have a stubby red clump that doesn’t cross the instability strip. Hence, few to no RR Lyrae stars.Hence, few to no RR Lyrae stars. It appears, however, that some metal rich GCs have extended HB.It appears, however, that some metal rich GCs have extended HB.

11. De Lee April 2004Michigan State University 2 nd Parameter Problem in Metal Rich GCs The existence of these GCs suggests that something beyond metallicity affects the morphology of the HB.The existence of these GCs suggests that something beyond metallicity affects the morphology of the HB. One set of possibilities involve helium enrichment (Sweigart & Catelan 1998) through various mechanisms.One set of possibilities involve helium enrichment (Sweigart & Catelan 1998) through various mechanisms. This leads to brighter HB and thus longer RR Lyrae Periods.This leads to brighter HB and thus longer RR Lyrae Periods.

12. De Lee April 2004Michigan State University NGC 6388 and 6441 NGC 6388 and 6441 are metal rich GCs that have extended HB that cross the instability strip.NGC 6388 and 6441 are metal rich GCs that have extended HB that cross the instability strip. Thus, they have significant numbers of RR Lyrae stars.Thus, they have significant numbers of RR Lyrae stars.

13. De Lee April 2004Michigan State University NGC 6388 [Fe/H] = -.60 ±.15[Fe/H] = -.60 ±.15 Total RRL = 14Total RRL = 14 =.71 d =.71 d =.36 d =.36 d N c /N Total =.57N c /N Total =.57 Values from Pritzl et al. 2002

14. De Lee April 2004Michigan State University NGC 6441 [Fe/H] = -.53 ±.11[Fe/H] = -.53 ±.11 Total RRL = 38Total RRL = 38 =.759 d =.759 d =.375 d =.375 d N c /N Total =.33N c /N Total =.33 Values from Pritzl et al. 2003

15. De Lee April 2004Michigan State University The Big Picture Both NGC 6388 and 6441 represent deviations from the Oosterhoff Dichotomy.Both NGC 6388 and 6441 represent deviations from the Oosterhoff Dichotomy. Metal rich and long average periods.Metal rich and long average periods. Contain RRab stars with periods .8 dContain RRab stars with periods .8 d (Catelan 2003)

16. De Lee April 2004Michigan State University Why NGC 6304? NGC 6304 is very metal rich [Fe/H] = -.59 (Zinn &West 1984).NGC 6304 is very metal rich [Fe/H] = -.59 (Zinn &West 1984). Several Previous Studies have found some RR Lyrae stars near NGC 6304. Rosino 1962, Terzan 1966, 1968, Hesser & Hartwick 1976, Hartwick, Barlow & Hesser 1981).Several Previous Studies have found some RR Lyrae stars near NGC 6304. Rosino 1962, Terzan 1966, 1968, Hesser & Hartwick 1976, Hartwick, Barlow & Hesser 1981). More recent studies (Valenti et al. 2003) have found new variables.More recent studies (Valenti et al. 2003) have found new variables.

17. De Lee April 2004Michigan State University Previous Work Hartwick, Barlow & Hesser Found 31 RR Lyrae stars near and around NGC 6304Found 31 RR Lyrae stars near and around NGC 6304 Although all of these were within the tidal radius, most were probably not members.Although all of these were within the tidal radius, most were probably not members. Valenti et al. Found 4 RRab stars and 2 RRc that she called likely cluster members. One of the RRab stars has the high period of.856 d

18. De Lee April 2004Michigan State University NGC 6304 [Fe/H] = -.59[Fe/H] = -.59 Total RRL = ?Total RRL = ? = ? = ? N c /N Total = ?N c /N Total = ? In 2002, we got data using ANDICAM on the YALO 1-m telescope at CTIO

19. De Lee April 2004Michigan State University A Tale of Two Methods To reduce this data, I will use two methods.To reduce this data, I will use two methods. Peter Stetson’s Daophot/Allframe method fits pseudogaussian point spread functions to each star.Peter Stetson’s Daophot/Allframe method fits pseudogaussian point spread functions to each star. C. Alard’s ISIS method uses image subtraction to identify variable stars.C. Alard’s ISIS method uses image subtraction to identify variable stars.

20. De Lee April 2004Michigan State University ISIS 2.1 In image subtraction, variable stars do not need to be fully resolved in order to find them.In image subtraction, variable stars do not need to be fully resolved in order to find them. This allows us to get much closer into the center of a GC.This allows us to get much closer into the center of a GC.

21. De Lee April 2004Michigan State University Allframe and ISIS Allframe ISIS Period.394 d.338 d

22. De Lee April 2004Michigan State University CM-Diagram Using Allframe

23. De Lee April 2004Michigan State University A Visual Picture The circle shows which stars were included in the CM Diagram.The circle shows which stars were included in the CM Diagram. The numbered stars are the RR Lyrae stars.The numbered stars are the RR Lyrae stars.

24. De Lee April 2004Michigan State University RR Lyrae Light Curves RR 11685 P =.467 d RR 9056 P=.338 d RR 5835 P=.394 d

25. De Lee April 2004Michigan State University More Light Curves RR 11563 P =.270 LPV 7980LPV 62966

26. De Lee April 2004Michigan State University Light Curves for RR 1932 b v P =.812

27. De Lee April 2004Michigan State University RR 1932 Cluster Membership Case For 1.Same V level as HB 2.Within tidal radius of GC 3.B and V are only averaged over 4 nights each Case Against 1.Too Blue, at least in preliminary CM 2.It is physically distant from the GC

28. De Lee April 2004Michigan State University Where to Go From Here? Recalibrate the variables on the CM diagram.Recalibrate the variables on the CM diagram. Use deeper variability cuts to find more variables.Use deeper variability cuts to find more variables. Use Image Subtraction to try to get closer into the core of NGC 6304.Use Image Subtraction to try to get closer into the core of NGC 6304.

29. De Lee April 2004Michigan State University References Alard, C. 2000, AA&S, 144, 363 Alard, C. & Lupton, R. H. 1998, ApJ, v. 503, p. 325 Freedman, W. L., et al. 2001, ApJ, 553, 47 Catelan, M 2003, astro-ph/0310159 Hartwick, F. D. A., Barlow D. J., & Hesser, J. E. 1981, AJ, 86, 1044 Hesser, J. E. & Hartwick, F. D. A. 1976, ApJ, 203, 113 Layden, A. C., Ritter, L.A., Welch, D. L., & Webb, T. M. A. 1999, AJ, 117, 1313 Pritzl B., Smith, H. A., Catelan, M, & Swigart, A. V. 2000, ApJ, 530, L41 Pritzl B., Smith, H. A., Catelan, M., & Swigart, A.V. 2001, AJ, 122, 2600 Pritzl B., Smith, H. A., Catelan, M., & Swigart, A.V. 2002, AJ, 124, 949 Pritzl B., Smith, H. A., Stetson, P. B., Catelan, M., Swigart A. V., Layden, A. C., & Rich, R. M. 2003, AJ, 126, 1381 Rosino, Asiago Contr 132 1962 Terzan, Publications de l'Observatoire de Haute-Provence, v. 9, no 1 1966 Terzan, Publications de l'Observatoire de Haute-Provence, v. 9, no 24 1968 Silbermann, N. A., Smith, H. A., Bolte, M., & Hazen, M. L. 1994, AJ, 107, 1764 Smith, H. A. RR Lyrae Stars, Cambrigde University Press, 1995 Stetson, P. B. 1987, PASP, 99, 191 Stetson, P. B. 1994, PASP, 106, 250 Stetson, P. B., et al. 1998, ApJ, 508, 491 Sweigart, A. V. & Catelan, M. 1998, ApJ, 501, L63 Valenti, E., Bellazzini, M., & Cacciari, C. 2003, in ASP Conf. Ser., 296, 404 Zinn, R. & West, M. J. 1984, ApJ, 55, 45