Variable SiO Maser Emission from V838 Mon

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Variable SiO Maser Emission from V838 Mon

• Mark Claussen
• May 16, 2006
• Nature of V838 Mon and its Light Echo

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Main Collaborators

• Howard E. Bond, STSci
• Sumner Starrfield, ASU
• Kevin Healy, ASU

May 16, 2006 V838 Mon Mtg
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Astronomical Masers

• Mainly OH, water, SiO, methanol
• Found in several different places in the
  universe
• Star-forming regions
• Circumstellar shells around late-type stars
• Active Galactic Nucleii
• Supernova Remnants
• V838 Mon
• Maser emission is bright, easy to observe
• Radiative transfer is non-linear, pumping schemes
  not always clear, so interpretation is not easy

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SiO Masers

• J 1? 0 rotational transitions in different
  vibrationally excited states (v 1, 2, and 3)
• These transitions occur at a wavelength of 7mm
  (43 GHz)
• Using the VLA (Very Large Array) we can obtain
  angular resolution ranging from 60 to 300 mas
  (depending upon configuration)
• Using the VLBA (Very Long Baseline Array), the
  angular resolution can be 500 microarcseconds
  (and astrometry even better)
• Also, radio spectroscopy easily reaches 0.1 km/s
  spectral resolution

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SiO Maser Emission from V838 Mon

• Non detection in Nov 2003
• First detected February 2005 (Deguchi et al.)
• VLA Monitoring begun in Sep 2005
• Position of SiO masers 07h 04m 04.824s -03d
  50 50.50 position is at least good to 10 mas,
  compares favorably to USNO stellar position
• Monthly since then (more or less)
• VLBA Observations October 2005, January 2006,
  March 2006
• Still under reduction

May 16, 2006 V838 Mon Mtg
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Other Radio Observations of V838 Mon

• GBT High Velocity Search for SiO Masers (/-350
  km/s, Oct 2005)
• no detected high velocity SiO masers
• VLA Search for Water Masers (monthly check with
  the SiO monitoring)
• no water masers detected
• VLA Search for v3 SiO (J1? 0) transition
  (March 2006)
• no v3 masers (to a 5-sigma detection limit of
  50 mJy/beam)
• VLA Radio Continuum Search at 8.4 GHz (March
  2006)
• no radio continuum detected (rms 30 uJy/beam at
  8.4 GHz)

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More Radio Observations

• VLBA Observations of SiO Masers
• Peak emission appears unresolved at 0.8
  milliarcseconds resolution, but only about 50 of
  the flux.
• Some hint of a spatial change across the line

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Results of Radio Observations

• No high velocity maser emission (not in a high
  velocity outflow)
• No v3 emission (no high excitation)
• No water masers --- pumping ? physical
  conditions ? no water molecules in the right
  place ?
• No radio continuum --- consistent with the
  possibility of ionization from B3 companion
• v1 and v2 masers are variable over month
  timescales

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Other places for SiO Masers

• Mira variables, late-type supergiants
• Pulsating stars
• Oxygen-rich shells harbor molecular masers
• OH, H2O, and SiO
• Masers can probe the kinematics and dynamics
  of the
• circumstellar shell

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28 mas
TX Cam SiO Masers (Diamond et al.)
v 1, J1? 0 transition Distance 450 pc Ring
diameter 28 mas 12.6 A.U.
SiO masers lie a few stellar radii outside the
stellar photosphere, but inside the dust
condensation zone.
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SiO Maser Properties in Mira Variables

• Collisional pumping / radiatve pumping ?
• A few (1-2) stellar radii from the stellar
  surface, inside the dust condensation zone
• Number density of molecular hydrogen of 5 x 109
  cm-3
• Temperature 1500 K
• Tangential amplification explains the rings
• Optical, IR and SiO masers are correlated over
  the optical light period
• SiO masers vary in phase with near and mid-IR
• Velocity extent of the maser emission 15 km/s
• Short-term variability ?
• Models require the Mira pulsation to explain
  temporal variability ?

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V838 Mon Masers, Mira Variables, and Parallax

• At a distance of 7 9 kpc, maser ring about 1.8
  mas in diameter barely resolvable by VLBI
• Turn-on of masers tell us something about pumping
  scheme --- favors radiative
• No pulsation ? So variability may not be similar
  to Miras
• VLBI of SiO masers holds the possibility of a
  parallax measurement as well.
• 50 uas accuracy per measurement epoch, with
  several epochs over a year should perhaps get to
  a parallax with rms errors of 15 or 20 uas,
  depending on systematics
• Maser polarization observations may tell us
  something about magnetic fields

May 16, 2006 V838 Mon Mtg