[Sci-all-l] Astronomy Student Colloquium

[davollbach at vassar.edu]

This Monday, October 2 at 3:00pm the department of Physics and Astronomy
will be presenting the first round of student talks of the year. 5
astronomy students will be giving brief presentations on the research that
they conducted over the summer. The talks will be in the lecture hall in
Sander's Physics. The students speaking and their abstracts follow.

Alex Burke, Vassar ‘07
X-RAY EMISSION FROM CLUMP BOW SHOCKS IN MASSIVE STAR WIND FLOWS

        Recent observations have shown that the emission profiles of
massive stars such as Zeta Pup and Zeta Ori have unusually hard
x-ray emissions, and the x-ray line profiles tend to be
symmetrical and only slightly blueshifted. We suggest a possible
explanation for this: in the highly supersonic stellar winds that
form around a massive star, locally denser regions of the wind
form axially symmetric bow shock structures. We treat these denser regions
as rigid spherical “clumps”, and assume that they exist
randomly around the star. The bow shock shape is parabolic, with
temperatures along the shock in excess of 10^6 K, decreasing from
a maximum temperature at the shock head. Taking into account
stellar occultation, clump occultation, and optical depth
parameters, we simulate the line profiles resulting from emission
along the shock. We reasonably reproduce the main features of the
observed line profiles, though some parameters, such as the speed
of the clumps, remain unclear at this time.

Ximena Fernández, Vassar ‘07
HI 21-cm and OH 18-cm Arecibo Observations of (Ultra)Luminous
Infrared Galaxies
Advisors: Drs. T. Ghosh, E. Momjian, C. Salter, (Arecibo Observatory)

I present the HI 21-cm and OH 18-cm spectral lines observations of
eighty-five luminous infrared galaxies from the 2 Jy IRAS-NVSS
sample. We detected HI in 82 galaxies (16 new detections), and OH in 7
galaxies (5 new detections). In some cases, the HI spectra showed the
classic Gaussian or double horn distributions, while the majority
exhibited distorted features indicating they are in interacting/
merging systems. IRAS 23327+2913 is discussed in greater detail since both
HI and OH are new detections, and its spectra display features that
indicate the presence of two nuclei at the beginning stages of
interaction.  This study hopes to contribute to the current
understanding of the differences between LIRGs with AGN and those
with pure starburst.

David Vollbach, Vassar ‘07
Rotation Periods of T tauri stars in NGC 1333
Advisor: William Herbst, Wesleyan University

Observations of NGC 1333 were conducted over the course of 6 winters at
the Van Vleck Observatory. Photometric analyses of 76 stars across 2
fields of view were able to determine rotation periods for 11 of these
stars. A method for combining periodograms from all 6 years of
observations by multiplication proved very successful in reducing noise
and clearly expressing periods.

Jenna Lemonias, Vassar '08
147 GHz / 157 GHz Methanol Line Ratios in Regions of Star Formation
Advisor: Dr. Vladimir Strelnitski, Maria Mitchell Observatory

We present line ratios for the methanol maser rotational transitions 90-81
A+ at 147 GHz and 7-1-60 E at 157 GHz for 8 sources.  DR21N, DR21 (OH),
NGC 7538M, NGC 7538S, NGC 7538W, NGC 7538IRS9, W75N, and W75N OFF, were
observed with the 12-meter radio telescope at Kitt Peak National
Observatory both on-site and remotely.  Maser emission was found in 7 of
these sources. Ratios of the 147 GHz line to the 157 GHz line show that
most sources have stronger emission in the 147 GHz line by a factor of 2. 
However, one source, DR21 (OH), has a ratio as high as 35.  Statistical
equilibrium calculations of the populations of the methanol rotational
levels are being performed in order to determine the probable physical
explanation of this deviation.  Preliminary analysis shows that the
147/157 ratio may be a steep function of the gas density and that the
unusually high 147/157 ratio for DR21 (OH) may signify an atypically high
density in the maser condensation.

The Effects of Interactions on Galaxy Evolution in the Early Universe
Thomas Ferguson, Vassar College ’07, Brendan Mullan, Colgate University
’07 Advisor:  Dr. Debra Elmegreen, Vassar  College

We study galaxies out to redshift of z~1.3, corresponding to a lookback
time of about 7 billion years, using data from the GEMS and GOODS sky
surveys taken by the Advanced Camera for Surveys (ACS) on the Hubble Space
Telescope (HST).  Of the 10,000 galaxies included in this survey, we
concentrate on a subset of pairs of interacting galaxies, and how the
interactions affect galactic evolution through changing morphologies and
star formation.  A subset of 51 interacting galaxies, known as “antennae,”
are characterized by bridges connecting the galaxies, and/or by long tidal
tails. Another 76 interacting galaxies, categorized as “shrimp,” exhibit
plumes of tidally perturbed galactic disk material. The extent of these
features is constrained by the extent, density, and, shape of the dark
matter halo around the interacting pair.  We determine several optical
properties of the galaxies, including isophotal contours, integrated
colors, magnitudes, linear sizes of tidal tails, fractional tail
luminosity, disk scale lengths, tail surface brightness, and star forming
clump masses and ages. The scale lengths for both samples generally are
1/3 to 1/5 times the diameter of the central disk. This is a scale length
range characteristic of nearby spiral galaxies. We have derived ages and
masses of 99 antennae clumps and 352 shrimp clumps by comparing our colors
and magnitudes with theoretical models of cluster evolution at different
redshifts. For both data sets, clump ages ranged from 107 to 5x109 years
and clump masses averaged  107 to 108 Mo.  The average V band surface
brightness of the tails is between 24 and 24.5 magnitudes, which is close
to our detection limit. About 1/3 of the antennae sample had maximum tail
lengths > 10 times the scale length, which constrains the dark matter halo
to no more than 10 times the luminous disk mass. In one galaxy, an
apparent dwarf galaxy at the end of a 50 kpc long tail may have formed as
a result of the interaction. A rarely observed event in merging galaxies,
the absolute magnitude of the tidal object, -15.9, matches well with
observed dwarf galaxies. The formation of such a massive end clump
requires a low to moderate mass halo that extends beyond the optical disk.