dsph in Local Group July 2014 Vienna

Transcription

1 John Menzies SAAO

2 dsph in Local Group Local Group associated with Galaxy, M31, within ~1 Mpc of centre of mass Galaxy has 25 companion dsph M31 has ~ 26 ~ 3 dsph not associated with either, near boundary dsph have relatively small mass in stars < 25x10 6 M Θ Contribute to construction of large galaxies (eg, Sgr dsph) Little or no current star formation July 2014 Vienna 2

3 AGB stars Brightest stars bolometrically in dsph, particularly prominent in NIR Post RGB evolutionary stage, undergoing mass loss to varying degrees (up to ~ fewx10-5 M Θ /yr) contribute significantly to ISM and later generation of stars most in dsph appear to be C stars, many are variable July 2014 Vienna 3

4 Photometric monitoring in J,H,K S of brightest accessible dsph with IRSF at SAAO, Sutherland Search for Variability in particular Patricia Whitelock, Michael Feast, Noriyuki Matsunaga and other Japanese colleagues July 2014 Vienna 4

5 Fornax Most massive MW dsph Extended SFH (deboer et al,2013,a&a,544,73) [M/H] range -0.6 to -2 Peak at -0.9 (Gullieuszik et al 2007) CM diagram: RGB with diagonal TRGB Numerous AGB stars extend to v red J-K SR variables, Miras Iscohrones 2Gyr, 10Gyr, [M/H] ~ -0.9 Whitelock P A et al. MNRAS 2009;394: July 2014 Vienna 5

6 Spectral types available for many stars C,S,M Shown on CM diagram and 2-colour diagram Extreme (H-K) colours cf LMC C stars Thick dust shells Dust mass-loss rate ~5x10-9 M Θ /yr (Lagadec et al 2008) Whitelock P A et al. MNRAS 2009;394: July 2014 Vienna 6

7 Stars with J-K S > 1.0 appear to be variable Typically 18 epochs of observation Std dev a measure of variability Amplitude increases towards redder colours (red points variables from optical (Bersier&Wood (2002)) Whitelock P A et al. MNRAS 2009;394: July 2014 Vienna 7

8 Variables SR Miras Non-periodic Whitelock P A et al. MNRAS 2009;394: July 2014 Vienna 8

9 Leo I Low-level star formation over a long period with a burst from 1-3 Gyr ago (Dolphin 2002) Very narrow distribution of [M/H], peaking at -1.2 (Gullieuszik et al 2002) CM diagram shows a well-populated AGB above a narrow RGB TRGB K S = AGB has C stars, SR and Mira variables Isochrones for 10Gyr and 2 Gyr with typical metallicity Menzies J W et al. MNRAS 2010;406:86-94 July 2014 Vienna 9

10 Two colour diagram for Leo I 2 colour diagram shows reddest stars significantly redder than LMC Dust shells Menzies J W et al. MNRAS 2010;406:86-94

11 Menzies et al 2002: 4 extremely red variables, positions but no periods determined we have not been able to find any relationship whatsoever between those coordinates and reality Held E V et al. MNRAS 2010;404: July 2014 Vienna 11

12 V image K image Held E V et al. MNRAS 2010;404: July 2014 Vienna 12

13 Miras Long-term trends Menzies J W et al. MNRAS 2010;406:86-94 Vienna 13

14 Sculptor Predominantly old population (deboer et al 2012) Some evidence of ~2Gyr population (Revaz et al 2009 Range of [Fe/H], -1 to -2, mean (Kirby et al 2009), tail to ~-3.0 CM diagram shows little AGB 2 Miras, 6 C stars below TRGB 3 v low metallicity Menzies J W et al. MNRAS 2011;414: July 2014 Vienna 14

15 C stars below TRGB Young, relatively metalrich? Isochrone 2Gyr [Fe/H]~-1.1 C/O >1 in black (Marigo et al 2008) Or extrinsic? Not variable Menzies J W et al. MNRAS 2011;414: July 2014 Vienna 15

16 Two-colour diagram for Sculptor MAG29 and V544 periods 554 and 189 d Mira MAG29 significantly red wrt LMC Period 554d suggests it is young Menzies J W et al. MNRAS 2011;414:

17 Sextans Very similar optical CM diagram to Sculptor Mean [Fe/H] = -1.9 (Lee et al 2009) 2 extremely metal-poor stars [Fe/H]<-3 2 Miras (Sakamoto et al 2012) periods 122 and 326 days longer period one is a C star(mauron et al 2004) Matsunaga, priv comm July 2014 Vienna 17

18 Carina Complex SFH, episodic Most stars formed in 2-6 Gyr episode, [Fe/H] -1.8 to -1.2 Old population >10Gyr [Fe/H]<-1.5 Unpublished CM diagram Field stars, RV members 9 C stars, 3 below TRGB, 3+ variable July 2014 Vienna 18

19 Leo II Predominantly old population ~9 Gyr (±2). Small intermediate age population (C stars) Low metallicity, mean [Fe/H] ~-1.7, some -1.1 CM diagram shows only C stars Above TRGB, one below One Mira, P=183d Gullieuszik M et al. MNRAS 2008;388:

20 Others in MW System Draco, Ursa Minor Old, similar SFH Carbon stars, at or below TRGB No LPV variable search Cetus, Tucana Tucana 2 old populations, different metallicities 7 possible LPV (@TRGB), No C stars Cetus Old population 1 possible LPV, 6 C stars, 3 below TRGB July 2014 Vienna 20

21 Sgr dsph Predominantly ~8 Gyr [Fe/H] -0.4 to -0.7 Some -0.25, some -2.0 Early NIR work selected from 2MASS (Whitelock et al 1999) 26 spectroscopic C stars; estimate total ~100 8 Miras Evidence for intermediate age population Lagadec et al C-rich stars, all Miras Batinelli & Demers 2013 Choose probable C stars (J-K) 0 >1.4 from 2MASS 12 new Miras + 13 other red variables McDonald et al 2012 Spectroscopically identified 5 S stars, 19 new C stars McDonald et al reddened AGB stars (J-K)>1.3, 21 LPV, no periods July 2014 Vienna 21

22 Galaxy Mass* M V * [Fe/H] * C stars Miras x10 6 M Θ Sgr dsph Fornax Leo I Cetus (3)? Sculptor (6) 2 Antlia ?? Leo II Tucana ? Sextans Carina (3) 0 Draco (6) 0 U Mi (7) 0 *McConnachie 2012 July 2014 Vienna 22

23 Mira Variables Distance Indicators Apart from Sgr dsph, dsph have 19 Miras. Same K-logP in LMC for both O- and C stars (Whitelock et al 2008) Also fits dsph Miras but effects of dust shells evident in some dsph Miras Bolometric corrections based on (J-K) colours (Whitelock et al 2006) M bol logp relation fits very well Important to use BC consistently As useful as Cepheids in infrared (Feast & Whitelock 2013) Both 50d Cep and 380d Mira have M K ~ -7.9 At 8μm, 50d Cep and 230d Mira: M 8 ~ -8.3; 380d Mira: M 8 ~-9.2 July 2014 Vienna 23

24 July 2014 Vienna 24

25 Galaxy Mass* M V * [Fe/H]* C stars Miras x10 6 M Θ And VII (2)? And II (1)? And I ? And VI (1)? And III (1)? And V ? And X XXIX <~ ?? *McConnachie 2012 July 2014 Vienna 25