Variable SiO Maser Emission from V838 Mon

Mark Claussen

May 16, 2006

Nature of V838 Mon and its Light Echo

Main Collaborators

Howard E. Bond, STSci

Sumner Starrfield, ASU

Kevin Healy, ASU

May 16, 2006 V838 Mon Mtg

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

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

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

• 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 v=3 SiO (J=1 0) transition (March 2006)

• no v=3 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)

May 16, 2006 V838 Mon Mtg

Other Radio Observations of V838 Mon

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

May 16, 2006 V838 Mon Mtg

Results of Radio Observations

• No high velocity maser emission (not in a high velocity outflow)

• No v=3 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

• v=1 and v=2 masers are variable over month timescales

May 16, 2006 V838 Mon Mtg

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

May 16, 2006 V838 Mon Mtg

OH

H2O

SiO

100 --- 10000 AU

100s of AU

Photosphere

SiO Masers and Dust Condensation Zone

A few stellar radii

TX Cam SiO Masers(Diamond et al.)

v = 1, J=1 0 transition

Distance ~450 pcRing diameter 28 mas = 12.6 A.U.

28 mas

SiO masers lie a few stellar radii outsidethe stellar photosphere, but inside thedust condensation zone.

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 ?

May 16, 2006 V838 Mon Mtg.

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