Double (X-ray) Vision:
The Close Binary, Accreting T Tauri System
V4046 Sgr
Joel Kastner
Center for Imaging Science,
Rochester Institute of Technology
Collaborators: Germano Sacco (RIT), David Huenemoerder (MIT), Thierry
Montmerle (Grenoble), and the V4046 Sgr XMM Large Project team;
David Rodriguez (UCLA), Thierry Forveille (Grenoble), Pierre Hily-Blant
(Grenoble), David Wilner (SAO/ CfA), Charlie Qi (SAO/ CfA)
Chandra & XMM imaging has made clear:
X-ray emission is a signature property of low-mass, pre-MS stars
Chandra X-ray image of the
Orion Nebula Cluster
(10-day COUP observation;
Feigelson et al. 2005)
Nearby (D < 100 pc) pre-MS stars of age
~10-30 Myr are particularly conspicuous
and easy to study in X-rays*
Kastner et al. (1997)
Zuckerman & Song (2004)
*Object of our NASA ADA program: use HEASARC X-ray archives to
uncover additional examples of such stars
(see Kastner, Zuckerman, & Bessell 2008, A&A 491, 829)
But…what is the nature of young-star Xray emission?
Ne IX: r, i,
f
O VII
Ne IX
HD 98800
(Kastner et al. 2002)
Top: from Huenemoerder et al. (2007)
Bottom: from Kastner et al. (2004)
TW Hya: after ~10 Myr, still accreting
material from a dusty, molecular disk
Top left: HST/NICMOS coronagraphic imaging
of the TW Hya disk (Weinberger et al. 2002)
Top right: JCMT radio molecular line spectra of
TW Hya (Kastner et al. 1997)
Left: Submillimeter Array velocity maps of CO
emission from TW Hya (Qi et al. 2004)
TW Hya: unusual, but not unique…
V4046 Sgr and TW Hya:
“separated at birth”*?
• Both T~4500 K, “isolated”, nearby, “old” T Tauri stars
– TW Hya: namesake of the TW Hya Association
• Age ~8 Myr, (Hipparcos) distance 56 pc
– V4046 Sgr: probable member of the beta Pic Moving Group
• Age ~12 Myr, distance 72 pc (Torres et al. 2006)
• Both display IR spectral energy distributions
characteristic of dusty circumstellar disks w/ inner
“holes”
– Strong mid-to-far-IR emission from cool dust (T < 300 K)
– Little or no near-IR emission from hot (T > 500 K) dust
• Both show evidence for ongoing accretion in visible,
UV, and X-ray regimes
– Star formation proceeds even as Jovian planets are forming (or
have formed)?
*with apologies to Spy Magazine…
V4046 Sgr and TW Hya: “separated at birth”?
Wavelength [A]
Left: visible/IR SEDs (courtesy J. Rhee, UCLA)
Above: X-ray gratings spectra (Guenther et al. 2006)
V4046 Sgr and TW Hya: “separated at birth”?!
V4046 Sgr: a Keplerian, circumbinary disk
SMA imaging of CO emission
QuickTime™ and a
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QuickTime™ and a
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Left: movie of velocity-resolved SMA CO images
(courtesy D. Rodriguez, UCLA)
Above: animation of a Keplerian molecular disk
(by RIT Digital Cinema student J. Traver)
V4046 Sgr: a Keplerian, circumbinary disk
SMA imaging of CO emission
Blue: P-V diagram
constructed from SMA
data
Red: best-fit Keplerian
disk model
(Rodriguez, Kastner,
Wilner & Qi 2010, ApJ,
submitted)
Regarding V4046 Sgr: there is one little
detail I haven’t reminded you about yet…
V4046 Sgr is a CLOSE BINARY star system!
Nearly equal-mass
components of ~0.9
Msun separated by
~9 Rsun (Stempels &
Gahm 2004);
system inclination
estimated at i ~ 35o
(Quast et al. 2000)
The rotating, inner, circumbinary disk
of V4046 Sgr
Left: Phase-resolved Balmer emission line monitoring of
V4046 Sgr
Above: Schematic diagram illustrating model to interpret
Balmer emission line profile variability
(from Stempels & Gahm 2004)
V4046 Sgr: XMM Large Project
T. Montmerle (PI) & a cast of dozens*…
• 300 ks total exposure w/ XMM/RGS
– Obtained in three 100 ks pieces in Sept. 2009
• Coverage of two consecutive orbits
• Well-spaced in orbital phase
• Goals:
– Phase-resolved X-ray spectroscopy of an accreting T Tauri system
• Take advantage of well-established star(s)-disk geometry of V4046 Sgr
– Phase-dependent changes in X-ray accretion diagnostics?
– Near-simultaneous optical spectroscopy, photometry,
spectropolarimetry
• Accurate phase determination
• Track EW & RV variations in optical absorption & emission lines
• Magnetic field mapping (ESPADONS)
• Preliminary results: some highlights…
– X-ray vs. optical light curve
– Emission measure distribution
– f/i ratios of He-like ions
* T. Montmerle (PI, LAOG), J. Bouvier, E. Alecian (LAOG), D. Huenemoerder (MIT), J. Kastner, G. Sacco (RIT), C. Argiroffi(UNIPA), A.
Maggio, F. Damiani (OAPA), M. Gudel (ETH, Zurich), M. Audard (Obs. Geneve) S. Gregory (Exeter), J. F. Donati (Toulouse), G. Wade (Kingston,
Canada), G. Hussain (ESO), V. Holzwarth (Freiburg), S. Alencar (UFMG)
V4046 Sgr XMM Large Project
preliminary results: X-ray vs. optical light curves
V4046 Sgr XMM Large Project
preliminary results: soft vs. hard X-ray light curves
V4046 Sgr XMM Large Project
preliminary results: emission measure distribution
(V4046 Sgr vs. TW Hya)
V4046 Sgr XMM Large Project
preliminary results: f/i ratios
V4046 Sgr XMM Large Project
preliminary results: variation of f/i ratios
TW Hya, V4046 Sgr…so what’s next?
Left: VLT/VISIR line profile of [Ne II] emission from V4046 Sgr (Sacco et al, in prep)
Right: APEX detection of CO orbiting MP Mus (Kastner et al., in prep)
Recall: Lx/Lbol increases during the first ~30-100
Myr of evolution, for low-mass stars
Ages ~10 Myr
Pre-MS stars
w/ ages <~1
Myr
Kastner et al. (1997)
Are we seeing the effects of pre-MS
X-rays on disk gas?
V4046 Sgr and TW Hya: evidence for
X-ray ionization of molecular disks…
Left: from Lepp & Dalgarno (1996)
“X-ray-induced chemistry of
molecular clouds”
Summary
• V4046 Sgr: “twin twin” to TW Hya
– Two of the half-dozen known examples of accreting T Tauri stardisk systems within ~100 pc
• Both show strong evidence for X-ray irradiation (possibly X-ray-induced
chemical evolution) of disk material
• XMM/RGS Large Project: preliminary results
– EMD dominated by low-temperature plasma
• Strikingly similar to TW Hya
– Plasma densities ~1012 cm-3; anticorrelated w/ termperature
• Strikingly similar to TW Hya
– Light curve shows broad modulation punctuated by flaring
• Variation of plasma density -- anticorrelated w/ X-ray modulation?