TIME: Thursday, 07th June 2007 at 11:00 am
PLACE: CSO Conference Room
SPEAKER: Dr. Huabai LI (Harvard-Smithsonian Center for Astrophysics)
TITLE : Does the Galactic Magnetic Field Anchor in Turbulent Giant
Molecular Clouds ?
ABSTRACT:
Various mechanisms of supporting self-gravitating interstellar clouds
and
regulating star formation have been invoked. Among which, the relative
importance between turbulence and magnetic fields has been long under
debated, largely owing to the lack of observational constraints on cloud
formation theories. The recent development of Submillimeter
polarimetry
offers a chance to map the field morphology from the bulk volume of a
molecular cloud. By comparing the observed morphology with those from
MHD simulations, we can estimate magnetic field strength relative to
turbulence.
I will present the data collected so far, and future observation plans
with
CSO and SMA, along with an introduction of the polarimeters used in
these
two observatories.
TIME: Wednesday, 27th June 2007
at 11:00am
PLACE: CSO Conference Room
SPEAKER: Professor Takeshi OKA (University of Chicago)
TITLE : H3+, a new
astrophysical probe, and revelation of warm and
diffuse gas near the Galactic center
ABSTRACT:
With a super-massive black hole at the core, the region
near the
Galactic center is the hub of activity. Emissions from radio to X-rays
and
the densities of stars and gas all peak in the region. It also harbors
the
Central Molecular Zone (CMZ), a region of radius ~ 200 pc which has
the highest concentration of molecules in the Galaxy. Our infrared
spectroscopic observations in the last five years have shown that
sightlines toward the CMZ have H3+ column densities that are
~ 10 times higher than the highest observed in the Galactic disk.
Using this richness of H3+ with its unique characteristics
as an
astrophysical probe, a new category of gas with high temperature
(~ 250 K) and low density (~< 100 cm^(-3)) has been
revealed in the
CMZ. Our observations of 8 sightlines toward bright infrared YSOs by
the UKIRT, Subaru, Gemini South, and VLT and their analyses suggest
that the gas is ubiquitous and has a high volume filling factor in the
CMZ. The relation between this newly found gas and previously known,
i. e., the cold (~ 50 K) and high density (~> 10^(4)
cm^(-3)) gas
observed
by radio emission of CO, CS, HCN and other molecules, the hot (10^(4-6)
K) gas with high electron densities (~ 10 cm^(-3)) inferred from hyper-
strong radio-wave scattering, and the ultra-hot (10^(7-8)K) gas emitting
X-rays is speculated.
TIME : Friday, 20th July 2007 at 11:00 am
PLACE : CSO Conference Room
SPEAKER : Dr. Neal J. EVANS II (The Univeristy of Texas at Austin)
TITLE : Star Formation:
From Cores to Disks
ABSTRACT:
I will highlight recent developments in the early stages of star
formation.
Observations with the Spitzer Space Telescope and complementary data
at other wavelengths have provided more complete samples of
star-forming
regions. These provide constraints on theoretical models of the origin
of the
initial mass function and evolutionary stages. The early stages of star
formation include the separation of dense cores from the background
molecular cloud, the evolution before point source formation, the
infall
onto the central source, and the formation of the disk. These events
are
usually associated with changes in the SED associated with the Class
System.
The large sample available from the Cores to Disks (c2d) program
provides
good statistics on the numbers of objects in various stages, and these
can
be used to estimate timescales.
TIME : Thursday, 4th October 2007 at 4:00 pm
PLACE : CSO Conference Room
SPEAKER : Melanie Leong (Caltech Submillimeter Observatory)
TITLE : Update to the CSO
Submillimeter Active Optics System
ABSTRACT:
The Caltech Submillimeter Observatory's (CSO's) Submillimeter Active
Optics System is an open loop real time system that corrects the dish
surface figure for imperfections and gravitational deformations as the
dish moves in elevation during observations. This improvement in
the telescope's aperture efficiency aids observations in the shorter
wavelengths, specifically in the 350-µm-wavelength range.
Simplicity, attention to detail, and perseverance were the keys to the
success of this unique system.
The CSO's primary is part of a Robert Leighton telescope design,
consisting of 84 hexagonal panels forming a 10.4-meter primary dish.
There are 99 steel rod standoffs that interface the backing structure
to the back of the primary. It is on these standoffs where
heating and cooling assemblies are mounted and implemented to lengthen
or shorten the standoffs to desired lengths.
Holography maps were used to build a correction table to determine the
amount of length and location of change on the primary.
Implementation of thermal electric devices enables the adjustability
for each standoff.
The CSO's Submillimeter Active Optics System has been in use since
February 2003. Since then, new discoveries of distant galaxies or
sharper detail of known objects have been obtained. These will be
presented during this talk.
By holography, the smoothness of the dish is better than 10 microns RMS
from zenith angles of 5 to 63 degrees. The present percent
improvement to the primary's surface is as high as 74%, with an average
of 60% improvement.
Preliminary performance improvements have been found to compensate for
SHARCII's new mounting location, from the Cassegrain focus to a second
Nasmyth location, N2. SHARCII is an 384 pixel submillimeter high
angular resolution camera.
TIME : Friday, 12th October 2007 at 11:00 am
PLACE : CSO Conference Room
SPEAKER : Dr. Evelyne Roueff (Observatoire de Paris)
TITLE : Hydrogenated/Deuterated
Species; Observations and Models
ABSTRACT:
Thirty interstellar and circumstellar molecules containing
deuterium
have been detected to date, with several doubly- and triply-deuterated
isotopologues. The fractionation ratio, defined as the ratio of
the
column density of a deuterated molecule to its hydrogen counterpart,
is
often found to be orders of magnitude higher than the elemental
abundance
ratio, which is typically from 1.5×10−5 to
2.3×10−5. This deuterium
enhancement results from chemical processes, which may involve both
gas-phase [1,2] and surface reactions [3]. Observational data and
detailed
gas-phase models will be reviewed. Particular emphasis will be put on
ortho/ para chemistry and on the role of deuterated hydrocarbons as
vectors
for deuteration. We also discuss the consequences of local
elemental
deuterium enhancements on molecular fractionation ratios [4].
[1] Roberts, H., Herbst, E., Millar, T.J., 2003, ApJ 591, L41,
Roberts, H., Herbst, E., Millar, T.J., 2004, A&A 424, 905
[2] Roueff, E. Lis, D., van der Tak, F.F.S., Gerin, M.,
Goldsmith,
P., 2005, A&A 438, 585
[3] Lishat, A., Biham, O., Herbst, E., 2004, MNRAS 348, 1055
[4] Roueff, E., Herbst, E., Lis, D., Phillips, T., 2007, ApJL in press.
last updated on 2007/06/28 by hs