Variable Stars in NGC 6304Variable Stars in NGC 6304

Nathan De Lee (MSU)Nathan De Lee (MSU)

Horace Smith (Advisor) (MSU)Horace Smith (Advisor) (MSU)

Barton Pritzl (Macalester College)Barton Pritzl (Macalester College)

Marcio Catelan (PUC)Marcio Catelan (PUC)

Allen Sweigart (GSFC)Allen Sweigart (GSFC)

De Lee April 2004 Michigan State University

OverviewOverview

• 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

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RR Lyrae VariablesRR Lyrae Variables

• Population II stars Population II stars (Age > 10 Gyr)(Age > 10 Gyr)

• Horizontal Branch Horizontal Branch StarsStars

• Radially PulsatingRadially Pulsating• Standard Candles Standard Candles

MMVV .6 .6

(Smith 1995)

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Bailey TypesBailey Types

• Based on light curve Based on light curve shapeshape

• RRab Fundamental RRab Fundamental ModeMode

• RRc First OvertoneRRc First Overtone

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The Oosterhoff DichotomyThe Oosterhoff Dichotomy

• In 1939, Oosterhoff In 1939, Oosterhoff noticed a division in noticed a division in GC RR stars.GC RR stars.

OOI OOI OOII OOII

<Pab> <Pab> .55.55dd .64.64dd

<Pc> <Pc> .32.32dd .37.37dd

NNRRcRRc/N/Ntotaltotal .17.17 .44.44

(Oosterhoff 1939)

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Other PropertiesOther Properties

• The Oosterhoff types are also metallicity The Oosterhoff types are also metallicity groups.groups.

• Oosterhoff type I have [Fe/H] > -1.7Oosterhoff type I have [Fe/H] > -1.7• Oosterhoff type II have [Fe/H] < -1.7 Oosterhoff type II have [Fe/H] < -1.7

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[Fe/H] Dichotomy[Fe/H] Dichotomy

(Smith 1995)

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Do we fully understand the Do we fully understand the Oosterhoff Groups?Oosterhoff Groups?

There are a several issues that have There are a several issues that have appeared in the story of the Oosterhoff appeared in the story of the Oosterhoff groups.groups.

First, the Oosterhoff dichotomy may be First, the Oosterhoff dichotomy may be particular to the Milky Way.particular to the Milky Way.

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Milky Way GCMilky Way GC

The Oosterhoff gap The Oosterhoff gap in this version of in this version of the Period the Period Metallicity Graph is Metallicity Graph is filled with GCs filled with GCs from the LMC.from the LMC.

(Catelan & Prizl 2004)

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Other IssuesOther Issues

• In general, metal rich GCs should have a In general, metal rich GCs should have a stubby red clump that doesn’t cross the stubby red clump that doesn’t cross the instability strip.instability strip.

• Hence, few to no RR Lyrae stars.Hence, few to no RR Lyrae stars.• It appears, however, that some metal rich It appears, however, that some metal rich

GCs have extended HB.GCs have extended HB.

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22ndnd Parameter Problem in Metal Parameter Problem in Metal Rich GCsRich GCs

• The existence of these GCs suggests that The existence of these GCs suggests that something beyond metallicity affects the something beyond metallicity affects the morphology of the HB.morphology of the HB.

• One set of possibilities involve helium One set of possibilities involve helium enrichment (Sweigart & Catelan 1998) enrichment (Sweigart & Catelan 1998) through various mechanisms.through various mechanisms.

• This leads to brighter HB and thus longer This leads to brighter HB and thus longer RR Lyrae Periods.RR Lyrae Periods.

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NGC 6388 and 6441NGC 6388 and 6441

• NGC 6388 and 6441 are metal rich GCs NGC 6388 and 6441 are metal rich GCs that have extended HB that cross the that have extended HB that cross the instability strip.instability strip.

• Thus, they have significant numbers of RR Thus, they have significant numbers of RR Lyrae stars.Lyrae stars.

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NGC 6388NGC 6388

• [Fe/H] = -.60 [Fe/H] = -.60 ± .15± .15• Total RRL = 14Total RRL = 14• <P<Pabab> = .71> = .71dd

• <P<Pcc> = .36> = .36dd

• NNcc/N/NTotalTotal = .57 = .57

Values from Pritzl et al. 2002Values from Pritzl et al. 2002

De Lee April 2004 Michigan State University

NGC 6441NGC 6441

• [Fe/H] = -.53 [Fe/H] = -.53 ± .11± .11• Total RRL = 38Total RRL = 38• <P<Pabab> = .759> = .759dd

• <P<Pcc> = .375> = .375dd

• NNcc/N/NTotalTotal = .33 = .33

Values from Pritzl et al. 2003Values from Pritzl et al. 2003

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The Big PictureThe Big Picture

• Both NGC 6388 and Both NGC 6388 and 6441 represent 6441 represent deviations from the deviations from the Oosterhoff Oosterhoff Dichotomy.Dichotomy.

• Metal rich and long Metal rich and long average periods.average periods.

• Contain RRab stars Contain RRab stars with periods with periods .8.8dd

(Catelan 2003)

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Why NGC 6304?Why NGC 6304?

• NGC 6304 is very metal rich [Fe/H] = -.59 NGC 6304 is very metal rich [Fe/H] = -.59 (Zinn &West 1984).(Zinn &West 1984).

• Several Previous Studies have found some Several Previous Studies have found some RR Lyrae stars near NGC 6304. Rosino RR Lyrae stars near NGC 6304. Rosino 1962, Terzan 1966, 1968, Hesser & Hartwick 1962, Terzan 1966, 1968, Hesser & Hartwick 1976, Hartwick, Barlow & Hesser 1981).1976, Hartwick, Barlow & Hesser 1981).

• More recent studies (Valenti et al. 2003) have More recent studies (Valenti et al. 2003) have found new variables.found new variables.

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Previous WorkPrevious Work

Hartwick, Barlow & Hartwick, Barlow & HesserHesser

• Found 31 RR Lyrae Found 31 RR Lyrae stars near and around stars near and around NGC 6304NGC 6304

• Although all of these Although all of these were within the tidal were within the tidal radius, most were radius, most were probably not probably not members.members.

Valenti et al.Valenti et al.• Found 4 RRab stars Found 4 RRab stars

and 2 RRc that she and 2 RRc that she called likely cluster called likely cluster members.members.

• One of the RRab stars One of the RRab stars has the high period has the high period of .856of .856dd

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NGC 6304 NGC 6304

• [Fe/H] = -.59 [Fe/H] = -.59 • Total RRL = ? Total RRL = ? • <P<Pabab> = ?> = ?

• <P<Pcc> = ?> = ?

• NNcc/N/NTotalTotal = ? = ?

In 2002, we got data using ANDICAM on the YALO 1-m

telescope at CTIO

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A Tale of Two MethodsA 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 Peter Stetson’s Daophot/Allframe method

fits pseudogaussian point spread functions fits pseudogaussian point spread functions to each star.to each star.

• C. Alard’s ISIS method uses image C. Alard’s ISIS method uses image subtraction to identify variable stars.subtraction to identify variable stars.

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ISIS 2.1ISIS 2.1

• In image subtraction, variable stars do not In image subtraction, variable stars do not need to be fully resolved in order to find need to be fully resolved in order to find them. them.

• This allows us to get much closer into the This allows us to get much closer into the center of a GC.center of a GC.

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Allframe and ISISAllframe and ISISAllframe ISIS Period

.394d

.338d

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CM-Diagram Using AllframeCM-Diagram Using Allframe

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A Visual PictureA Visual Picture

• The circle shows The circle shows which stars were which stars were included in the CM included in the CM Diagram.Diagram.

• The numbered stars The numbered stars are the RR Lyrae stars.are the RR Lyrae stars.

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RR Lyrae Light CurvesRR Lyrae Light CurvesRR 11685 P = .467d RR 9056 P=.338dRR 5835 P=.394d

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More Light CurvesMore Light Curves

RR 11563 P = .270 LPV 7980 LPV 62966

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Light Curves for RR 1932Light Curves for RR 1932

b vP = .812

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RR 1932 Cluster MembershipRR 1932 Cluster Membership

Case ForCase For

1.1. Same V level as HBSame V level as HB

2.2. Within tidal radius Within tidal radius of GCof GC

3.3. B and V are only B and V are only averaged over 4 averaged over 4 nights eachnights each

Case AgainstCase Against

1.1. Too Blue, at least in Too Blue, at least in preliminary CMpreliminary CM

2.2. It is physically It is physically distant from the GC distant from the GC

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Where to Go From Here?Where to Go From Here?

• Recalibrate the variables on the CM Recalibrate the variables on the CM diagram.diagram.

• Use deeper variability cuts to find more Use deeper variability cuts to find more variables.variables.

• Use Image Subtraction to try to get closer Use Image Subtraction to try to get closer into the core of NGC 6304.into the core of NGC 6304.

De Lee April 2004 Michigan State University

ReferencesReferencesAlard, C. 2000, AA&S, 144, 363Alard, C. 2000, AA&S, 144, 363Alard, C. & Lupton, R. H. 1998, ApJ, v. 503, p. 325Alard, C. & Lupton, R. H. 1998, ApJ, v. 503, p. 325Freedman, W. L., et al. 2001, ApJ, 553, 47Freedman, W. L., et al. 2001, ApJ, 553, 47Catelan, M 2003, astro-ph/0310159 Catelan, M 2003, astro-ph/0310159 Hartwick, F. D. A., Barlow D. J., & Hesser, J. E. 1981, AJ, 86, 1044Hartwick, F. D. A., Barlow D. J., & Hesser, J. E. 1981, AJ, 86, 1044Hesser, J. E. & Hartwick, F. D. A. 1976, ApJ, 203, 113Hesser, J. E. & Hartwick, F. D. A. 1976, ApJ, 203, 113Layden, A. C., Ritter, L.A., Welch, D. L., & Webb, T. M. A. 1999, AJ, 117, 1313Layden, A. C., Ritter, L.A., Welch, D. L., & Webb, T. M. A. 1999, AJ, 117, 1313Pritzl B., Smith, H. A., Catelan, M, & Swigart, A. V. 2000, ApJ, 530, L41Pritzl B., Smith, H. A., Catelan, M, & Swigart, A. V. 2000, ApJ, 530, L41Pritzl B., Smith, H. A., Catelan, M., & Swigart, A.V. 2001, AJ, 122, 2600Pritzl B., Smith, H. A., Catelan, M., & Swigart, A.V. 2001, AJ, 122, 2600Pritzl B., Smith, H. A., Catelan, M., & Swigart, A.V. 2002, AJ, 124, 949Pritzl B., Smith, H. A., Catelan, M., & Swigart, A.V. 2002, AJ, 124, 949Pritzl B., Smith, H. A., Stetson, P. B., Catelan, M., Swigart A. V., Layden, A. C., & Rich, R. M. 2003, AJ, Pritzl B., Smith, H. A., Stetson, P. B., Catelan, M., Swigart A. V., Layden, A. C., & Rich, R. M. 2003, AJ,

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