Transcript HCN Near IK Tau and TX Cam

HCN Near
IK Tau and TX Cam
Kevin Marvel
American Astronomical Society
Waikoloa Beach Outrigger Resort
Kona-Kailua, Hawaii
Monday July 1, 2002
Evolved Stars by Radio
• AAVSO members have long aided
professional astronomers by observing
long period variable stars
• Radio Astronomers tuned their early
receivers to laboratory predicted
frequencies of molecules
• One type of source that shows interesting
molecular emission are the long period
variables (Miras, AGB Stars etc.)
AAVSO Data
Evolved Stars
• Have moved beyond the hydrogen burning
stage (and into a pulsating stage of He
burning)
• Have large luminosities due to their large
radii (measured in AUs!)
• Are cool in temperature (~ 2000K )
• Have extended “shells” around them
formed after dust condenses and is slowly
(5-30 km/s) pushed away from the star
Dust Emission - CSO
Dust Emission - Keck
Molecular Shells
• Due to the cold temperatures and large
quantities of molecules, chemistry can
take place
• The particular chemistry that does exist in
the shells is governed by whether there is
more carbon or oxygen in the shell
• Carbon-rich sources have many different
molecules, oxygen-rich have fewer
Different Shells Example
BIMA Data
A View of CO near TT Cyg
• Image made with the
IRAM telescope, a
millimeter array
• Shows the CO gas
• Diameter of shell is
half a light-year (!)
• CO “puffed” out from
central star about
6,000 years ago
• Still expanding…
The IRAM Telescope
HCN in O-rich Stars
• Early single dish work showed that there was
often HCN associated with O-rich stars
• This shouldn’t happen because all available C
bonds with all available O and the leftover
determines the chemistry of the star
• Chemical models were made that claimed that
methane could be formed near the central star,
blown outward and transformed to HCN through
exposure to UV light and some chemical
reactions
My task: test the models…
…with the OVRO telescope
(that has some interesting art)
The model
• Methane condenses relatively near the
star and is blown outwards
• When exposed to more UV light, it breaks
up and makes other molecules
• HCN is produced along with methanol and
CCH
• We know that HCN is there, but nobody
had ever looked for the other molecules
The Observations
• Done in winter/spring 1997-1998
• Several configurations of the OVRO
telescopes
• Observed transitions of HCN, methanol
and CCH
• Basic result: no CCH, no methanol
• Advanced result: first ever maps of the
HCN distribution in the star, could help
future model-makers
HCN Maps
• Radio data is often presented as contour
maps
• Higher contour levels mean more light
coming from the source
• Since molecular emission is emitted at
only particular frequencies, the Doppler
effect shifts the received frequency for gas
that is moving towards or away from us
TX Cam
HCN Shell Size
• To determine the shell size, I fit 2-dimensional
Gaussians (elliptically-shaped hills) to the
emission at the “zero” velocity
• The “zero” velocity gas is expanding directly in
the plane of the sky and represents the true
diameter of the distribution
• Also placed upper limits on the abundances for
methanol and CCH, which are much better than
with a single dish telescope (resolution effect)
TX Cam Shell Size
What else is going on near these
Stars?
• Masers…SiO, water and OH
• With the VLBA they can be tracked over
time
• Also, the kinematics of the gas shells
themselves can be studied
• New results seem to indicate that the
shells are rotating or at least have
interesting dynamics going on
R Aqr – Boboltz et al.
TX Cam – SiO masers Diamond et al.
Maser Animation
Conclusions
• A millimeter wavelength search for CCH
and methanol around TX Cam and IK Tau
turned up nada, forcing model-makers to
think again
• First ever HCN maps of TX Cam and IK
Tau gave size of distribution and that it is
centrally condensated, again important for
model-makers