Multi-object spectroscopy of massive stars in the Local Group and beyond

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L. Kaper

Multi-object spectroscopy of massive starsin the Local Group and beyondLex Kaper, Univ.of Amsterdam, Netherlands(with Alex de Koter, Lucas Ellerbroek, Chris Evans, Olga Hartoog, Rolf Kudritzki,Bertrand Lemasle, Bram Ochsendorf, Hugues Sana, Frank Tramper)


The most massive stars• Most luminous and hottest stars dominate energy(copious UV radiation) and momentum (stellar winds,supernovae) budget of the interstellar medium.• Key players in the chemical evolution of the Universe.• Progenitors to the most violentphenomena (gamma-ray bursts)detectable up to z ≥ 8.• Produce neutron stars andblack holes.• Likely the first stars weremassive stars.Can be observed at large distances;directly, or by their ionizing fluxpowering large H II regions.


Key questions to be addressed• How massive is the most massive star?- Stability; total mass parent cloud (IMF)• How are the most massive stars formed?- Radiation pressure; ionized gas; accretion rate;magnetic fields• How do the most massive stars evolve?- Rotation rate; metallicity• Which stars become neutron starsand which black holes?- Progenitor evolution; supernovamechanism (SN/GRB); NS EoS


The most massive stars(Crowther et al. 2010, MNRAS 408, 731)• Should be located in high mass (> 10 4 Mo), veryyoung (< 2 Myr) star clusters• Visually the brightest stars in their host clusters(L ~ M 1.5 )• Possess very powerful stellar winds- Spectral appearance more likely O supergiantor Wolf-Rayet like (de Koter et al. 1997,Crowther 2007) than O2/O3 V.No observational upper mass cutoff (e.g. Massey 2003) a limit close to 150 Mo (Weidner et al. 2004, Figer 2005)


Crowther et al. (2010)


Comparison to LMC-metallicity MS modelsCrowther et al. (2010)


Evidence for stars with M init > 150 MoCrowther et al. (2010)


BD+40 o 4220: Bohannan & Conti (1976)


Bohannan & Conti 1976, ApJ 204, 797


Formation of the most massive stars(i) How are the most massive stars formed?(ii) What are the physical properties of the newly formedstars?- Photospheric parameters- Rotational characteristics- Radiation-driven winds- Remnant stellar disc(iii) Are massive YSOs actively accretingand how do these objects relate tothe “dusty/gaseous disc” systems? Study ionizing stars of the youngest(ultra-)compact H II regions withVLT/X-shooter, SINFONI, CRIRES,and analyze their spectra


How to make a massive star?(a) A dense, rotating central disk of dust and gas, and a highly collimatedsupersonic outflow (accretion model) (b) Stars collide and merge to form ahigh-mass star (coalescence model). Whitney 2005, Nature News & Views


Formation of massive stars by accretionChieffi et al. (1995):Evolution of accretingstar starting from aninitial mass of 1 Mo,for different accretionrates Accreting star wouldappear little differentin L and T eff than amain-sequence starof fixed mass.Keto & Wood (2006)


Very Large Telescope, Cerro Paranal, Chile


VLT/X-shooterThe most powerful optical/near-IR spectrograph


Central star powering UCHIIIonizing star G29.96: O5 – O6.5 V(Watson & Hanson 1997)Spectral type consistent with L bol ,N Ly_cont , NIR photometry, nebularLines; no accretion/disc signaturesMartin-Hernandez et al. (2003)


Vela C Molecular CloudHill & Motte (2012, Herschel)


Massive YSOs in RCW36Ellerbroek et al. 2011, ApJ 732, L9Alex CarciofiVLT/X-shooter spectra


Accretion history “massive” YSOsEllerbroek et al. 2013, A&A in press


Mass loss and accretion diagnosticsEllerbroek et al. (2013)


HH1042 jet: ballistic modelv 0 cos i 170 km/sT 0 83.0 yrv 1 cos i 40 km/s28.5 yrT 1see also Raga et al. 2012for RR34Ellerbroek et al. (2013)


Massive stars are born as giants: B275 in M17Hoffmeister et al. (2008)


B275: massive YSO in M17B275Hanson et al. (1997)


SED B275:SpType B0 VL ~ 20,000 Lod = 1.98 ± 0.14 pc(radio parallax;Xu et al. 2011)Hanson et al. (1997)


Hanson et al. (1997)WHT La Palma


VLT/X-shooter spectrum M17-B275Ochsendorf, Ellerbroek et al. 2011, A&A 536, L1


FASTWIND models B7 III


B275: “bloated” PMS star contracting to MSB275 is on its way tobecome a 6 – 8 Mo starStill surrounded by diskOchsendorf et al. 2011


Massive stars in external galaxiesNGC 602 in SMC (HST)


VLT/FLAMES Tarantula Survey(Evans et al. 2011) ~1000 O stars22nd Anniversary ofHubble Space Telescope May 2012HST-GO 12499 (PI: D.A. Lennon)


MOS meeting A'dam, October 2012 32


Triggered star formation by 30 Dor


IC1613


Tramper et al. 2011, ApJ 741, L8


He II 4686HalphaPredicted mass-loss ratesas a function of decreasingmetallicity are too lowTramper et al. (2011)


First VLT/X-shooter spectrum of massive starsoutside Local Group: NGC 55


Hartoog et al. 2012,MNRAS 422, 367


Obtaining spectra of O stars in Local Group (and beyond)M V ~ -6Resolving power R ~ 10,0001.22λ/DLimiting mag m V ~ 21 VLT/X-shooter 0.03”~ 25 E-ELT/OPTIMOS-EVE 0.006”Distance(kpc)m VSeparation 0.3 pc(arcsec)SMC 68 13.2 1IC1613 730 18.3 0.09Cen A 4000 22.0 0.017Virgo cluster 16000 25.0 0.004


40Telescope developmentDiametermirror (m)E-ELT105VLT01600 1700 1800 1900 2000 2100


Extremely Large Telescope


OPTIMOS-EVEOPTIMOS-EVE


Chapman et al. (2006)Richardson et al. (2008)


Image Credits: David Radburn-Smith


ANGST SurveyDalcanton et al. (2009)NGC 247~3.4MpcAn ELT-MOS is essential for studies ofGALAXY EVOLUTION with the E-ELTNGC 300~1.9Mpc


Cerro Armazones, site E-ELT


E-ELT MOS• Explore E-ELT’s large field of view: 10’ x 10’• Obtain optical-NIR spectra of several hundredtargets in one shot• At low-level AO (OPTIMOS-EVE, high multiplex) orhigh-level AO (EAGLE, high definition) MOSAICOPTIMOS-EVEEAGLE


Evans et al. Proc. SPIEarXiv:1207.0768


RSG J-band spectra in Virgowith S/N ~ 200in 1 night E-ELT


galaxies out to 4Mpc➡ number of observable targets ~100© Ben Davies


➡ E-ELT: galaxies out to 35Mpc (modest...)➡ number of observable targets increased to~1500!!© Ben Davies


Conclusions• With the E-ELT it will become possible to study massivestar populations in a representative sample of galaxies(up to the Virgo cluster) in a way similar to current Galactic(and MC) studies.Extra-galactic astronomy and astrophysics will merge.• Current observations with e.g. X-shooter andFLAMES/GIRAFFE show the potential of such studies(and deliver already very important results).• It is obvious that at distances in and beyond the LocalGroup multi-object spectroscopy is the way forward(certainly if the amount of telescope time is limited).


Conclusions• With the E-ELT it will become possible to study massivestar populations in a representative sample of galaxies (upto the Virgo cluster) in a way similar to current Galactic(and MC) studies. Extra-galactic astronomy andastrophysics will merge.• Current observations with e.g. X-shooter and FLAMES/GIRAFFE show the potential of such studies (and deliveralready very important results).• It is obvious that at distances in and beyond the LocalGroup multi-object spectroscopy is the way forward(certainly if the amount of telescope time is limited).


E-ELT instrumentation

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