Star and Planet Formation Discussion Group
  Seminars and astro-ph

2010-2011:  Bryant conference room (217), Wed. 2:00 p.m.-3:00 p.m.
(astro-ph session if no speaker noted)

Fall 2011 schedule

Sep. 7
Katie Morzinski (University of Arizona)
Abstract Direct imaging of faint objects around bright stars is challenging
because the primary star’s diffracted light can overwhelm low-mass
companions.  Nevertheless, advances in adaptive optics (AO) and
high-contrast imaging have revealed the first pictures of extrasolar
planets.  In my dissertation I explore pathways to better understand
planetary systems via direct imaging.  First, I qualify MEMS deformable
mirrors for wavefront control in the upcoming Gemini Planet Imager
(GPI).  Micro-electro-mechanical systems (MEMS) technology allows for
thousands of degrees of freedom and represents a significant cost
efficiency over conventional glass deformable mirrors.  I prove these
high-order MEMS mircomirrors in the lab as well as on sky.  Second, I
use current state-of-the-art AO technology at Keck and Lick
Observatories to image brown dwarf companions to Hyades stars.  I
refine the LOCI PSF-diversity algorithm and achieve contrasts down to
10^{−5} on 1-minute Keck AO snapshots of 85 targets.  I discover
3 new brown dwarfs in the Hyades, as well as 36 low-mass stellar
companions in 30 systems.  There is a preference for lower-mass
primaries among the wider companions, which is difficult to explain as
the Hyades cluster is dynamically evolved after 625 Myr.  This research
into LOCI techniques and MEMS technology gives us confidence that GPI
will ultimately be successful in imaging and characterizing new
exoplanets directly.


Spring 2011 schedule  

January 19 Kei Tanaka (Tokyo Institute of Technology) -- Wed. 19th Jan. 2pm Bryant 217
Abstract In the formation of massive stars, radiation pressure acting the dust grains exceeds gravitational force. This strong radiation pressure would disturb mass accretion.  The radiation pressure is thought to act strongest at first absorbed region, i.e. behind the dust sublimation front. To overcome this direct stellar radiation feedback, it is argued that the ram pressure with high accretion rates is needed. Although it is thought that feedback on dust sublimation front is critical, most of resent simulations working on radiation pressure problem did not resolve innermost dust-free region (>2000K). To investigate the radiation pressure problem at the dust sublimation front, we calculate the innermost dust-free disk structure.

In this work, we analytically calculate the structures of the dust-free disks, taking into account the gas opacity. In the result the innermost disks exceed 10000K, and become radiation dominated disk.  And the dust-free disk is optically thick for large parameter range. Thus, the dust sublimation front would be shielded by the optically thick dust-free disk from direct stellar feedback, and accretion flow do not halted there.
Feb. 23
Phil Myers (CfA):  How do clusters get their stars?
Abstract We review the problem of star formation in clusters, and present new models  for star-forming condensations in clusters. Two hybrid models are presented, which are spherical on small scales and filamentary on large scales.  In and around clusters, cores embedded in linear filaments match the elongation of cluster gas, and the  central concentation of low-mass stars. In cluster centers, condensations require a low volume filling factor to produce massive stars with short spacing.  These may have stellate shape, where cores are nodes of filamentary networks, as seen in some simulations of colliding flows.  A simple criterion can distinguish the "isolated" mode where one core makes one star, and the "clustered" mode where one clump makes many stars.  A dense configuration of  stellate condensations may be indistinguishable from a clump forming multiple protostars via filamentary flow paths.

Winter/Spring 2010 schedule  

Mar. 4 Chip Kobulnicky (UWYO)

Intermediate-Mass Star Formation: Bridging the Gap Between High-Mass and
Low-Mass Regimes

Abstract High-mass star formation appears unlikely to be simply a scaled-up
version of low-mass star formation.  Additional factors such as
turbulence or cloud collisions may be necessary to produce the high
cloud densities necessary to rapidly deposit the gas needed to form a
very massive star.  Straddling the boundary between these two regimes
are Intermediate-Mass Star Forming Regions (IMSFRs): clumps forming, at
most, a 2-8 solar mass star.  Lacking the ionized gas and concomitant
thermal radio emission, such regions have escaped study, partly for lack
of suitable detection methods.  Using infrared surveys we identify and
investigate a small sample of probable IMSFRs.  In this pilot study, we
focus on the luminosities, cloud masses, and stellar content of these
innocuous regions that may hold clues as to what physical conditions
enable or constrain the transition from low-mass to high-mass star
Feb. 16 (Tue.)
Todd Bradley (University of Central Florida)

An Overview of the Bolocam Galactic Plane Survey (BGPS) and GBT Observations of Dense Cores in the Galactic Plane
The Bolocam Galactic Plane Survey (BGPS) has resulted in acquiring measurements at 1.1 mm continuum emission of dense cores over 170 square degrees in the galactic plane. The survey is contiguous from -10.5 < l < 90.5 and -0.5 < b < 0.5. The survey also includes coverage near l=111, the W3/4/5 complex, IC1396, and the Gem OB1 complex, resulting in approximately 8400 cores that have been measured. Follow up observations of some of the cores has been done using the Green Bank Telescope (GBT) where NH3 has been observed. Doppler shifting of spectral lines, line width, and relative strengths of NH3 emission lines may be used to constrain distance, optical depth, and velocity dispersion of NH3 within the core and thus serves as an excellent tracer to aid in constraining core properties as a whole. An overview of the BGPS and GBT observational campaigns will be given. Also, derived masses of representative cores from this investigation are compared with those derived from other surveys as a means of validating techniques used for mass determination.
Feb. 4
Keivan Stassun (Vanderbilt)

Empirical Constraints on the Formation and Evolution of Low-Mass Stars and Brown Dwarfs: A Panchromatic and Data-Intensive Approach


Jan. 21
Dan Whalen (CMU)

January 14 Mario Juric (CfA)

Mapping the Milky Way with SDSS
With the advent of open, large, astronomical surveys such as the SDSS, or the (planned) LSST, important discoveries that used to depended on access to large telescopes are now within reach of anyone, anywhere, and at any time. The key to making them is in knowing what data is available, what questions can it answer, and how to transform the terabytes of data to useful bits of information. In this seminar, I will use the Milky Way (sub)structure studies to illustrate the methods, both simple and complex, that produced important discoveries about the structure and formation of our Galaxy years after the underlying data became public. Similar concepts may be applicable to future datasets, or in different areas of astrophysics.

Fall/Winter 2009 schedule  

Nov. 12
Adam Kraus (Caltech)

Stellar Multiplicity and Planet Formation

Oct. 15
James De Buizer (Stratoshperic Obseravtory for Infrared Astronomy)

Unexpected Observational Properties of Massive Young Stellar Objects in the Mid-Infrared

Oct. 1 Betsy Barton (UC Irvine)

Star Formation and Gas in the Lowest-Density Environments

Sep. 17 Phil Armitage (U. Colorado - Boulder)

Planet Scattering with Small Body Disks

August 20 Tsevi Mazeh (Tel Aviv Univ.)

TODCOR (and TRICOR):  How to derive radial velocities from composite spectra

Winter/Spring 2009 schedule

April 30
Dan Whalen (LANL), Rafael Guzman, Jonathan Tan (UF)

Discussion on: The First Stars

April 23 Mike Butler (UF)

The Structure of Dense Cores: Probing the Initial Conditions of Massive Star Formation

Yichen Zhang (UF)

SEDs and Images from Radiation Transfer Code for Massive Star Formation

March 26
Franz Bauer (Columbia)

The Nature of the Faint Radio Source Population in the Chandra Deep Fields


The depth and breadth of the pan-chromatic coverage in the Chandra Deep
Fields is unrivaled over the entire sky, and includes extremely deep 20cm
and mid-IR surveys. Since radio and mid-IR emission are considered robust
tracers of star formation (e.g., the radio-IR correlation), these datasets
can be used to improve our overall understanding of star-forming galaxies
out to z~1.5. I will discuss some preliminary results to identify and
constrain the nature of the faint uJy radio source population, touching
upon the potential evolution of radio-IR correlation and problems with AGN

March 5
Greg Bryan (Columbia)

On Transition from Population III to Population II Stars

January   30

UF-UCF Star & Planet Formation Day


January 29
Sarah  Dodson-Robinson (EXScI, JPL)

Planets, Silicon & Iron:
How to isolate the relationships between several correlated variables with the K-S bootstrap test


I present a new statistical method, the K-S bootstrap test, that isolates the relationship between two random variables when both quantities are known to correlate strongly with a third random variable. The problem arose as follows: I wanted to find out whether giant planets mainly orbit stars with high silicon abundance, rather than stars with low silicon abundance. (Since giant planet cores are composed mainly of silicate rock, silicon-rich star systems should form planets much more easily than silicon-poor systems.) However, a star's silicon content is strongly correlated with its iron content, and astronomers have observed that planets usually orbit iron-rich stars. I needed a way to test my hypothesis that silicon-rich star systems readily form planets, while making sure I wasn't just re-discovering the known planet-iron correlation.
    Here I describe the statistical analysis that led to the discovery that stars with planets are indeed silicon-rich, independent of their iron content. I also discuss applications of the K-S bootstrap test to other areas of science. For example, the K-S bootstrap test could help answer the following questions:
* How effective is tobacco-prevention education? School districts with aggressive anti-smoking curricula may be preferentially located in areas with high cigarette taxes, which also discourage smoking.
* Is obesity truly a cause of heart disease? Many people labeled "obese" according to height-weight charts have normal blood pressure and cholesterol, eat healthful diets and get regular exercise. Answering this question requires isolating the various influences of genetics, diet, exercise, thyroid function and more.

Peter Anders (Utrecht)

A New Challenge to Old Clusters

Fall/Winter 2008 schedule

December 4
Joshua Pepper (Vanderbildt)

KELT and the Search for Transiting Exoplanets


I will talk about the current state of exoplanet discovery,
giving a brief background about the field, and focusing on transit
surveys.  I will talk about the KELT survey for transiting exoplanets, and
about the coming collaboration between KELT and MARVELS.
The talk will be broadly based, explaining the science of transits at a
basic level, and discussing the basic questions about searching for
exoplanets and the power of transits.  I will place KELT in the context of
the current state of the field.

November 20
Jessica Lu (Caltech)

A discussion of kinematics in star forming regions

Suggested reading

Kinematic Structure of the Orion Nebula Cluster and its Surroundings

November 6
Alberto Bolatto (Maryland)

Spitzer Surveys of the SMC

October 24-25
UF-UCF Starformation Day


October 2
Alice Quillen (Rochester)

Spitzer observations of Cen A's Nuclear shell and models for episodic star formation


Spitzer observations of Centaurus A have revealed a kpc sized shell-like
structure in its center. I will explore possible scenarios accounting for
the spectral and morphological properties of the shell. I will review a
wide range of observational settings that suggest that star formation can
be episodic. Some observations of galaxies imply that due to feedback,
star formation can approach a self-regulating steady rate. Other settings,
such as the central kpc of Centaurus A, imply that episodes of enhanced
star formation can be followed by periods of quiescence. Using simple
differential equation models previously used to model biological population
dynamics, I will account for these two behaviors, and classify models
according to parameters describing feedback and gas consumption. Future
applications of these and similar models may be powerful.

Sept 18
Steinn Sirgudsson (Penn State)

Post-colloquium discussion on Exotic Earths

Sept 4
Eric Ford, Dimitri Veras(UF)

Overview of the "Extra-solar planets in multi-body systems" conference,
held August 25-29 2008 in Torun(Poland)

Conference page

Winter/Summer 2008 schedule

July 17
Welcoming new SPF folks

June 5
Eric Ford, Dimitri Veras, Scott Fleming (UF)

Summary of the IAU Symposium on Transiting Planets

IAU Symposium 253, Boston, May 19-23 2008

April 17 Nadya Gorlova (UF)

Free discussion / Article review

Suggested reading

Disk around an old star (2008 Zuckerman et al.)

On the Binary Nature of Dust-encircled BD+20 307 (2008 Weinberger)

April 10
David Bennett (Notre Dame)

Microlensing Planet Search

March 20
Cynthia Gomez Martin (UF)

Article review

Suggested reading

Hubble Space Telescope NICMOS Observations of NGC 1333: The Ratio of Stars to Substellar Objects (Greissl et al. 2007 AJ)
March 13
Nadya Gorlova (UF)

Summary of the winter school "Early Phases of Planet Formation"

School page with downloadable presentations

February 14
Regular meeting

February 1

UF-UCF Starformation Day


January 17

Discussion of AAS and the Starformation Newsletter
(Dec 2007 issue)

Suggested reading

SF Newsletter page

Fall/Winter 2007 schedule

Novemver 29
Brian Lee (UF)

Selection of Target Stars for MALRVELS (a Radial Velocity Planet Survey)

Novemver 15 Nadya Gorlova (UF)

On the Correlation Between Stellar Mass and Planet Incidence (article review)

Suggested reading

A new planet around M dwarf: revealing a correlation between exoplanets and stellar mass
Johnson et al. (astro-ph / 16 Jul 2007)

Planet formation around stars of various masses: the snow line and the frequency of giant planets
Kennedy & Kenyon (astro-ph / 4 Oct 2007)

Novemver 1
Dimitri Veras & Suvrah Mahadevan (UF)

Summary of the DPS Meeting in Orlando

October 11 Fabian Heitsch (Michigan)


October 04
Eric Ford (UF)

Characterizing the Orbital Eccentricities of Transiting Extrasolar Planets with Photometric Observations


The discovery of over 200 extrasolar planets with the radial velocity        
(RV) technique has revealed that many giant planets have large
eccentricities (Butler et al. 2006), in striking contrast with most
of the planets in the solar system and prior theories of planet
formation.  The realization that many giant planets have large
eccentricities raises a fundamental question: ``Do terrestrial-size
planets of other stars typically have significantly eccentric orbits
or nearly circular orbits like the Earth?''  On one hand, the idea
that our solar system is special appears to fly in the face of the
Copernican principle. On the other hand, most of the known giant
planets of FGK stars have sizable eccentricities, and these
eccentric giant planets would inevitably perturb the orbits of any
nearby terrestrial planets.  Here, we demonstrate that photometric observations
of transiting planets could be used to characterize the orbital eccentricities for
individual transiting planets, as well the eccentricity distribution for various
populations of transiting planets (e.g., those with a certain range of orbital
periods or physical sizes).  Such characterizations can provide valuable
constraints on theories for the excitation
of eccentricities and tidal dissipation.  We outline the
future prospects of the technique given the exciting prospects for
future transit searches, such as those to be carried out by the CoRoT
and Kepler missions.