1 / 36

Stellar Life-Cycles in Chandra Observations of the Galactic Center

Stellar Life-Cycles in Chandra Observations of the Galactic Center. Michael Muno (UCLA/Hubble Fellow). N. E. Chandra Observations of our Galaxy. Wang, Gotthelf, & Lang 2002; NASA/UMass. 30 pc. N. E. Chandra Observations of our Galaxy.

gilda
Download Presentation

Stellar Life-Cycles in Chandra Observations of the Galactic Center

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Stellar Life-Cycles in Chandra Observations of the Galactic Center Michael Muno (UCLA/Hubble Fellow)

  2. N E Chandra Observations of our Galaxy Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

  3. N E Chandra Observations of our Galaxy We see thousands of X-ray sources in a sea of diffuse emission. Our goal is to identify the natures of the point sources in order to: • Provide a census of accreting compact objects and young stars. • Address the nature of the diffuse X-ray emission. • (Eventually) study the physics of X-ray production. Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

  4. N E Chandra Observations of our Galaxy Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

  5. N E Sgr A* 5 pc Baganoff et al. (2003); Muno et al. (2003a, ApJ, 589, 225)

  6. X-ray Point Sources • 2287 sources have been resolved. • About 200 are in the foreground of the Galactic center. • About 40 are background AGN • Sources have LX=1030-1033 erg s-1 =10-9 - 10-6LEdd. Muno et al. (2003a, ApJ, 589, 225)

  7. X-ray Sources Trace the Stellar Population The surface density of X-ray sources falls off as R-1, just like the stellar population in the infrared.

  8. Predictions for the Population • Pfahl, Rappaport, & Podsiadlowski (2002) predict ~100 HXMBs in our field. • Belczynski & Taam (2004) predict a similar number of LMXBs. see also Iben et al. 1997, Howell et al. 2001, Bleach 2002, Willems & Kolb 2003, Cheng et al. 2004 Tauris & van den Heuvel (2004)

  9. Predictions for the Population Questions: • The efficiency of the common envelope phase. • Whether accretion-induced collapse can form neutron stars. • What compact objects accreting at low rates look like. • The duty cycle of transient outbursts from accretion disks. Tauris & van den Heuvel (2004)

  10. Galactic X-ray Point Sources See also A. Bykov’s talk on supernova fragments.

  11. Spectra of the Point Sources keV Color = (H-L/H+L). L = 3.3-4.7 keV H = 4.7-8.0 keV Muno et al. (2004b, ApJ, 613, 1179)

  12. Spectra of the Point Sources mCV HMXB pulsar WR/O, LMXB YSO, RS CVn CV Muno et al. (2004b, ApJ, 613, 1179)

  13. Spectra of the Point Sources Muno et al. (2004b) • Lines are observed from He-like and H-like Fe, which could result from a 8 keV thermal plasma or a photo-ionized plasma. CVs exhibit similar spectra.

  14. Periodic X-ray Modulations • Eight sources show modulations. • Periods between 300s and 4.5h • Amplitudes > 45% rms • Seven have hard spectra (HR > 0.1) • Consistent either with magnetically accreting WD or NS. Muno et al. (2003c, ApJ, 599, 465)

  15. Point Sources and Diffuse X-ray Emission Muno et al. (2004a, ApJ, 613, 326)

  16. Spectrum of Diffuse Emission Muno et al. (2004a) • Lines from Si, S, and Ar are consistent with a 107 K plasma. • Lines from Fe could be from a 108 K plasma, but they also resemble those from the point sources.

  17. Number-Flux Distribution • The log(N)-log(S) distribution is very steep: slope a=-1.7 • >105 undetected sources would be required to produce the observed diffuse emission. • Only ~104 CVs should be present in the field. Muno et al. (2004a)

  18. Point Sources and Diffuse X-ray Emission • No known class of point source can account for the (apparently) diffuse X-ray emission. • The intensity of the diffuse emission varies spatially. • See talk by R. Belmont to find out what we think the diffuse emission really is. Muno et al. (2004a, ApJ, 613, 326)

  19. Reasons to Do Better • Although bright, hard CVs have been observed in the Galactic plane, observations of globular clusters do not reveal similar sources. • Age effect? • There should be a significant population of younger objects, such as HMXBs and WR/O stars.

  20. Finding Young, Massive Stars Multi-wavelength Observations: • 2MASS: J,H,K to a depth of K<11 • SIRIUS/IRSF (South Africa): J,H,K to a depth of K<13 (Nagata and Nishiyama) • NICMOS: J,H,K, Pa-alpha to K<17 (Archival) • KECK: J, H, K, Br-gamma to K<19 (Morris/Muno) • VLA: 8.4 GHz to a depth of 1 mJy (Bowers) For comparison, CVs should have K<21, and HMXBs and WR/O stars should have K<17.

  21. Diffraction-limited Keck Observations 104 total foreground sources 1”

  22. Diffraction-limited Keck Observations 104 total foreground sources 1” Confusion makes IR surveys inefficient for identifying countperparts.

  23. Sources with Radio Counterparts G. Bower; Muno et al. (2005) • Found two X-ray sources with radio and IR matches. • One is a known massive, young star in an HII region (H2). 8.4 GHz

  24. Million-Solar Luminosity Stars Thanks to Adam Burgasser • IR spectra reveal lines from H and He characteristic of winds from stars with T >15,000 K, often classified as B[e], Of, and LBV stars. • Steve Eikenberry has found another object that may be an HMXB. • The fact that these are isolated has important implications for star formation.

  25. Sgr A* 5 pc Searching for X-ray Binaries • We identified accreting black holes and neutron stars by looking for sources that: • varied by at least a factor of 10, and • had peak luminosities >1034 erg s-1. • We found 7 such systems.

  26. Sgr A* 5 pc Searching for X-ray Binaries • We identified accreting black holes and neutron stars by looking for sources that: • varied by at least a factor of 10, and • had peak luminosities >1034 erg s-1. • We found 7 such systems. Neutron Star LMXB GRS 1741.9-2858 Muno et al. (2005, astro-ph/0412492)

  27. An Overabundance in the Central Parsec • Four lie within 1 pc of Sgr A*. The enclosed stellar mass is 2 106 Mo. • Three lie between 1-25 pc of Sgr A*. The enclosed stellar mass is >3 107 Mo. • Transients are over-abundant by >20x in the inner parsec! Muno et al. (2005) 1 pc

  28. An Overabundance in the Central Parsec D. Porquet will explain how we know this one is an LMXB. Muno et al. (2005) 1 pc

  29. 1 pc 47 Tuc LMXBs Are Also Concentrated in Globular Clusters Keel et al. Grindlay et al. 2001; Pooley et al. 2003 Optical: 1.5 m telescope in Chile X-ray: Chandra In globular clusters, LMXBs are over-abundant by a factor of 100 per unit stellar mass.

  30. Dynamical Friction • Lighter objects tend to collect in the wakes of heavier ones. • As a result, the heavier object is slowed down. • The heavier object loses energy, and falls deeper into the gravitatational potential.

  31. 1 pc Dynamically Forming LMXBs Grindlay et al. 2001; Pooley et al. 2003 47 Tuc simulation by E. Pfahl In globular clusters, LMXBs are over-abundant by a factor of 100 per unit stellar mass.

  32. 1 pc 47 Tuc Dynamically Forming LMXBs • rc = 6 104 Mo pc-3 • s = 12 km s-1 • rc = 7 106 Mo pc-3 • s = 70 km s-1

  33. Dynamically Forming LMXBs • 104 black holes have dynamically settled into the central pc (Morris 1993, Miralda-Escudé & Gould 2000). • Pfahl & Loeb (in prep.) estimate that these form LMXBs via binary-single interactions at a rate of 10-6 yr -1. • Over the dynamical time scale of 10 Gyr, 103 LMXBs could form. simulation by E. Pfahl; Muno et al. (2005)

  34. Sgr A* Young HMXBs • Several dozen massive stars formed among 104 stars 7 Myr ago. • Up to 300 black holes may have already formed. • At most 10% of these could be in HMXBs, or on order 30 systems. 1 pc Muno et al. (2005) Infrared laser guide-star image courtesy W.M. Keck Observatory.

  35. Conclusions • The vast majority are CVs that trace the old stellar population. • Known stellar populations cannot account for the diffuse emission, unless they are overabundant by a factor of 10 near the GC. • Radio and IR observations have identified two young, million-solar luminosity stars. • An overabundance of X-ray transients in the central parsec provides evidence for a concentration of stellar- mass black holes in the central parsec .

More Related