BEGIN:VCALENDAR VERSION:2.0 PRODID:-//jEvents 2.0 for Joomla//EN CALSCALE:GREGORIAN METHOD:PUBLISH BEGIN:VTIMEZONE TZID:America/Chicago BEGIN:STANDARD DTSTART:20190121T120000 RDATE:20190310T030000 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:America/Chicago CST END:STANDARD BEGIN:STANDARD DTSTART:20191103T010000 RDATE:20200308T030000 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:America/Chicago CST END:STANDARD BEGIN:STANDARD DTSTART:20201101T010000 RDATE:20210314T030000 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:America/Chicago CST END:STANDARD BEGIN:STANDARD DTSTART:20211107T010000 RDATE:20220313T030000 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:America/Chicago CST END:STANDARD BEGIN:STANDARD DTSTART:20221106T010000 RDATE:20230312T030000 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:America/Chicago CST END:STANDARD BEGIN:STANDARD DTSTART:20231105T010000 RDATE:20240310T030000 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:America/Chicago CST END:STANDARD BEGIN:STANDARD DTSTART:20241103T010000 RDATE:20250309T030000 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:America/Chicago CST END:STANDARD BEGIN:STANDARD DTSTART:20251102T010000 RDATE:20260308T030000 TZOFFSETFROM:-0500 TZOFFSETTO:-0600 TZNAME:America/Chicago CST END:STANDARD BEGIN:DAYLIGHT DTSTART:20190310T030000 RDATE:20191103T010000 TZOFFSETFROM:-0600 TZOFFSETTO:-0500 TZNAME:America/Chicago CDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20200308T030000 RDATE:20201101T010000 TZOFFSETFROM:-0600 TZOFFSETTO:-0500 TZNAME:America/Chicago CDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20210314T030000 RDATE:20211107T010000 TZOFFSETFROM:-0600 TZOFFSETTO:-0500 TZNAME:America/Chicago CDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20220313T030000 RDATE:20221106T010000 TZOFFSETFROM:-0600 TZOFFSETTO:-0500 TZNAME:America/Chicago CDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20230312T030000 RDATE:20231105T010000 TZOFFSETFROM:-0600 TZOFFSETTO:-0500 TZNAME:America/Chicago CDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20240310T030000 RDATE:20241103T010000 TZOFFSETFROM:-0600 TZOFFSETTO:-0500 TZNAME:America/Chicago CDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20250309T030000 RDATE:20251102T010000 TZOFFSETFROM:-0600 TZOFFSETTO:-0500 TZNAME:America/Chicago CDT END:DAYLIGHT END:VTIMEZONE BEGIN:VEVENT UID:a516d3079b14782b2d40b88ad9baf285 CATEGORIES:Stars, Planets, and ISM Seminar SUMMARY:Stars, Planets, and ISM Seminar LOCATION:PMA (RLM) 15.216B DESCRIPTION;ENCODING=QUOTED-PRINTABLE:
Title: TBA
DTSTAMP:20240328T054601Z DTSTART;TZID=America/Chicago:20200122T120000 DTEND;TZID=America/Chicago:20200122T130000 SEQUENCE:0 RRULE:FREQ=WEEKLY;UNTIL=20200507T000000Z;INTERVAL=1;BYDAY=WE TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT UID:a516d3079b14782b2d40b88ad9baf285 CATEGORIES:Stars, Planets, and ISM Seminar SUMMARY:Steven Janowiecki, The University of Texas at Austin LOCATION:PMA (RLM) 15.216B DESCRIPTION;ENCODING=QUOTED-PRINTABLE:How To Get the Most Science Out Of Your HET Observations
DTSTAMP:20240328T054601Z DTSTART;TZID=America/Chicago:20200122T120000 DTEND;TZID=America/Chicago:20200122T130000 RECURRENCE-ID;TZID=America/Chicago:20200122T120000 SEQUENCE:0 TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT UID:a516d3079b14782b2d40b88ad9baf285 CATEGORIES:Stars, Planets, and ISM Seminar SUMMARY:Special Seminar - Sean Johnson, Princeton University LOCATION:PMA (RLM) 15.216B DESCRIPTION;ENCODING=QUOTED-PRINTABLE:Observing Galaxy Feeding and Feedback in the Circum/inter-ga lactic Medium in Emission and Absorption Across Cosmic Time p>
Near-Field Cosmology with Stellar Abundances p>
Of Worlds to Come: Exoplanets with Extreme Precision Spectro scopy
We are ex oplanet hunters, anchored for now to the only habitable planet we know of, around a relatively well-behaved yellow star. Other Earths have remained el usive, hidden deep within the noise of their own stars, and the limitations of our techniques. To overcome these challenges we adopt a multidisciplina ry approach encompassing stellar and planetary physics, cutting edge instru mentation, and innovative data analysis techniques. Based on our technologi cal and scientific advancements in the last decade, the field of radial velocity (RV) exoplanet detection is now poised to enter an exciting new phase. Currently in build+commissioning phases are p lanet hunting Doppler spectrographs aiming at <30cm/s RV precision in th e optical in quest for Earth analogs, and <1m/s in the NIR in pursuit of M dwarf planets. These massive instruments leverage a range of technologic al advances, from high-homogeneity illumination delivery setups, to sophist icated wavelength calibration, ultra stable environmental control, and prec ision software pipelines. In this talk I will outline the state of the field in the context of six new planet hunting instruments I am wor king on, describe the challenges we have overcome, and look forward to the rich rewards we can consequently expect -- incl uding an unprecedented understanding of stars, and the spectroscopic direct detection of planetary atmospheres from the ground.
Spring Break
DTSTAMP:20240328T054601Z DTSTART;TZID=America/Chicago:20200318T120000 DTEND;TZID=America/Chicago:20200318T130000 RECURRENCE-ID;TZID=America/Chicago:20200318T120000 SEQUENCE:0 TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT UID:a516d3079b14782b2d40b88ad9baf285 CATEGORIES:Stars, Planets, and ISM Seminar SUMMARY:Chris Sneden, The University of Texas at Austin LOCATION:PMA (RLM) 15.216B DESCRIPTION;ENCODING=QUOTED-PRINTABLE:Iron-group Elemental Abundances in Very Low Metallicity Star s: A Fresh Look
What gets us into trouble is not what we don't know. It's what we know for
sure that just ain't so." (Mark Twain)
Starting from the mid 1990s w
e have believed much observational evidence pointing to non-solar abundance
ratios of iron-group elements in very metal-poor halo stars. There are dee
p declines in [Cr/Fe], [Mn/Fe], and [Cu/Fe], and large increases in [Co/Fe]
. In this talk I will suggest that such trends either do not exist or at be
st are much more mild than previously supposed. High resolution spectra of
a small set of stars with metallicities [Fe/H] ~ -3 have been gathered with
HST/STIS and ground-based facilities and have been analyzed with fresh lab
oratory transition data to conclude that: (a) the most reliable Fe-group ab
undances depend on study of ionized-species spectra; (b) abundances from ne
utral-species "popular" resonance lines need large NLTE corrections; and (c
) significant correlated variations in [Sc,Ti,V/Fe] from star to star exist
not only in our data set but in previous investigations - just not much no
ticed. I will discuss steps in broadening our work to a large survey now un
derway.
Multi-Wavelength Monitoring of Strong Rotational Modulations from the Young L-dwarf Companion VHS1256b
Heterogeneous clouds in the atmospheres of brow n dwarfs and exoplanets introduce wavelength-dependent rotational modulatio ns in their light curves. High-precision time-resolved observations of the rotational modulations can reveal condensate cloud properties such as altit ude and covering fractions, which are essential constraints on cloud format ion and atmospheric circulation models. Using HST/WFC3 grism spectroscopy a nd Spitzer time-resolved observations, we found that VHS1256b, a low surfac e gravity substellar companion that spectroscopically resembled HR8799bcd p lanets, is variable at the 25% level in its near infrared light curves. Thi s is among the strongest variability amplitudes that have ever been discove red in a substellar object. In this talk, I will summarize the observationa l results from multi-wavelength time-series observations of VHS1256b. I wil l then discuss the interpretations of the results by comparing the chromati c variations in the modulation amplitude to the ultra-cool atmospheric mode ls. Our observations agree with the predictions from patchy cloud models, s upporting the theory of dissipation of clouds in photospheres as the source of the rotational modulation.
Frank Mills, Australian National University
Th
e diversity of planetary atmospheric chemistry: Lessons and challenges from
our solar system and extrasolar planets
Atmospheres in our solar system range from oxidizing to re ducing, transient to dense, veiled by clouds to transparent. Observations a lready suggest that exoplanets exhibit an even more diverse range of atmosp heric chemistry and composition. Nevertheless, there are commonalities acro ss the atmospheres of our solar system that provide valuable guidance and l essons for observing and interpreting exoplanetary atmospheres. Lessons gle aned from decades of study of planetary atmospheric chemistry are synthesiz ed and explored to understand their implications for exoplanets.
Tyler Nelson, The Universi
ty of Texas at Ausitn
Title: TBA
SECOND YEAR DEFENSE
Galaxy Formation with the Milky Way
The Milky Way is an excellent test bed for Galaxy formation. In recent years new observations have led to a better understanding of the central co mponent of our Galaxy, the bulge. This includes the discovery of a metal-po or population of stars, which simulations predict may be the oldest stars i n the Galaxy. In this talk I will present results from the COMBS (Chemical Origins of Metal-poor Bulge Stars) survey, which aims to chemodynamically c haracterize this metal-poor bulge population. Specifically, I will talk abo ut the first part of this survey that was published last year which present s the chemical abundances of 24 metal-poor bulge stars using high-resolutio n (R~47,000) VLT/UVES spectra along with the upcoming second part of the su rvey which looks at the dynamics of ~500 metal-poor bulge stars. I will als o speak about my work making a high precision map of the distant Milky Way using red clump stars selected from photometry and how this map can be used to further our understanding of how the Milky Way and similar galaxies for med.
No talk scheduled
DTSTAMP:20240328T054601Z DTSTART;TZID=America/Chicago:20200325T120000 DTEND;TZID=America/Chicago:20200325T130000 RECURRENCE-ID;TZID=America/Chicago:20200325T120000 SEQUENCE:0 TRANSP:OPAQUE END:VEVENT BEGIN:VEVENT UID:a516d3079b14782b2d40b88ad9baf285 CATEGORIES:Stars, Planets, and ISM Seminar SUMMARY:2 Talks LOCATION:PMA (RLM) 15.216B DESCRIPTION;ENCODING=QUOTED-PRINTABLE:Ronan Kerr, The University of Texas at Austin
Mapping the Progression of Star Formation in the Solar Neighborhood
The Sco-Cen OB asso ciation is the nearest site of recent large-scale star formation to the sun (100- 150pc) and contains roughly 10000 members. Due to its diversity, lar ge size, complex star formation history, and relative accessibility due to distance, Sco-Cen provides an ideal environment in which to study the outpu t of star formation prior to dissipation into the galactic disk. With the m ost recent data from Gaia DR2, it is now possible to study the star-formati on history and substructure of Sco-Cen in detail. I have used Gaia photomet ry and parallaxes to identify young stars using an isochrone-generated mode l stellar population. Analyzing all high-quality Gaia stars with parallax & gt; 3 mas, I have identified about 16000 stars on the pre- main sequence wi th photometric ages of less than 30 Myr, and Gaia proper motion measurement s reveal that nearly 5200 of these are members of Sco-Cen. Preliminary resu lts reveal new insights into sub-clustering within Sco-Cen, which will help to uncover and describe the formation, motion, and subsequent dispersal of these stars throughout the region’s history. I also identify a set of youn g stellar associations from my catalog of young stars, adding to a diverse web of recent star-forming sites in the solar neighborhood.
Jessica Luna,
The University of Texas at Austin
Investigating the Mine
ralogy of Clouds in Brown Dwarf Atmospheres
Melanie Rowland, The University of Texas at Austin
Mapping Water Ice and Silicates in Interstellar Clouds Using Broadband
Photometry
Th e variation of extinction with wavelength is one of the best tracers of the nature and composition of dust grains. Particularly important is the natur e of grains in dense molecular clouds since these environments are sites of star formation. The composition of these grains may be inferred from infra red spectra, but undertaking a spectroscopic survey is time intensive, and relevant space-based facilities are no longer operational. A new broa dband photometric technique to estimate 3.0-micron water-ice and 9.7-micron silicate optical depths utilizing archived imaging observations from the W ide-field Infrared Survey Explorer (WISE), Spitzer Space Telescope, and Two Micron All-Sky Survey (2MASS) will be presented. The technique has t he advantage of capitalizing on data already on-hand for thousands of stars behind more than a dozen nearby quiescent and star-forming molecular cloud s. I will present this technique, discuss its benefits and limitation s, and characterize correlations of these optical depths with extinction. p>
Kyle Franson, The
University of Texas at Austin
Enhancing Direct Imag
ing of Substellar Companions through Hipparcos-Gaia Astromet
ric Accelerations
In this talk, I will present two applications of long time-baselin e astrometric accelerations from Hipparcos and Gaia&nb sp;to direct imaging of exoplanets and brown dwarfs. I’ll first discus s the measurement of a dynamical mass of the brown dwarf HD 984 B. The mass es of directly-imaged substellar objects are traditionally inferred from&nb sp;their age and luminosity through low-temperature cooling models. This le ads to highly uncertain masses that are dependent on the choice of model an d initial conditions assumed. Model-independent, dynamical masses prov ide a valuable empirical test of these models and their underlying physics. These gold standards are difficult to obtain; only ten brown dwarfs a nd giant planets have dynamical masses. HD 984 exhibits a proper motion cha nge between Hipparcos and Gaia, which enables us to measure the dynamical mass of its brown dwarf companion, in conjunction with relative orbital motion. To enable effective orbit fitting, we obtaine d a new epoch of the system with NIRC2 on Keck in July, 2019. I will r eport on the current status of this measurement and the reduction of the ne w observation. I’ll then briefly discuss the beginnings of a survey of young, accelerating systems to search for new giant planet companions. Lar ge direct-imaging surveys have revealed that giant planets on wide orb its are rare, with occurrence rates around 1%. Astrometric accelerations pr esent the opportunity to improve these outcomes by focusing future cam paigns on stars that exhibit astrometric reflux motion consistent with the existence of a companion. We are currently commencing a survey of promising accelerating systems. I’ll discuss the structure of this survey and s ome of the considerations made in constructing the sample.
SECOND YEAR DEFENSE
The Effect of Bin ary Stars on Measurements of the Initial Mass Function
< !-- START: Sliders -->The initial mass function (IMF) defines the mass distribution of a population of newly-formed < span class="gmail-il">stars, and is useful as a diagnostic of < span class="gmail-il">star formation physics. Most evidence ind icates that the IMF is mostly universal, but some star forming regions, like Taurus, are discrepant with that universal IMF. One explanation for this discrepancy is unrecognized and unm odeled stellar multiplicity. Unresolved binary stars in variably extincted and spatially extended regions may not have the age or mass corresponding to their apparent position on an HR diagram. Binaries are often expensive or impossible to identify via observa tions (e.g., high-resolution imaging or spectroscopy) and thus are not easi ly screened from samples. In lieu of traditional observations, I have carri ed out a synthetic low-resolution optical spectroscopic survey of a young&n bsp;star-forming region to investigate the ef fect of unresolved binary stars on derived population statistics, including the IMF. My simulated population i ncludes unresolved close binaries, and I determine each system’s apparent e ffective temperature and luminosity using spectral fitting. Then, I use evo lutionary models to infer an age and a mass for each system, allowing me to explore the apparent age and mass distribution produced by a population in cluding unresolved multiplicity.I will present the initial results of this synthetic study, including the potential biases that may have been in troduced into the IMF by past surveys of young stellar populations.
David Guszejnov, The University of Texas at Austin
Star Formation in GMCs: Introducing the STARFORGE simulations
Margot Fitz Axen, The University of Texas at Austin
Numerical Propagation of Low Energy Cosmic Rays from Protostellar Accre
tion Shocks
In the densest regions of molecular clouds ionization comes primarily f rom cosmic rays (CRs), charged particles accelerated to relativistic energi es. Observations show that the ionization rate is higher than expected insi de molecular clouds, suggesting that low-energy CRs are accelerated locally by the shocks associated with star formation. However, the cosmic ray flux cannot be observed directly from specific sources outside of our solar nei ghborhood, and previous studies on the subject have primarily been carried out analytically with simplifying assumptions about the cloud properties. W e developed a method for modeling CR transport in molecular clouds numerica lly, using a fully 3D grid-based Monte Carlo transport code. We use numeric al magnetohydrodynamic simulations of the magnetic field and gas density ar ound forming stars as inputs for our code and follow the propagation of the CRs accelerated at the accretion shock, taking into account energy losses. We find that the CR flux exhibits a beaming effect, with the CRs tending t o follow magnetic field lines and lose energy when they enter a higher dens ity area. This results in certain regions, such as the lower density outflo w cavity around the protostar, having a higher CR flux and resultant ioniza tion rate than the surrounding regions.
SECOND YEAR DEFENSE
Establishing the Epoch of Giant Planet Migration: Near-Infrared Jitter of Young Sun-like Sta rs
Th e presence of giant planets interior to the ice lines of Sun-like stars ind icates that inward orbital migration is likely a common phenomenon. However , the processes by which these gas giants arrived at their present-day loca tions are poorly constrained because radial velocity and transit surveys ha ve largely avoided young stars. As a result, our knowledge of giant planet statistics is largely confined to old ages (~1-10 Gyr) after most migration has terminated. This second year research project aims to improve our unde rstanding of how and when giant planets m igrate to small separations. In 2018 we launched a precise RV survey of 119 intermediate-age (~50-250 Myr) GK dwarfs with the Habitable Zone Planet Fi nder spectrograph (HPF) at McDonald Observatory's Hobby Eberly Telescope to determine the timescale and dominant physical mechanism of giant planet mi gration. This report summarizes results from the first 14 months of this pr ogram, with a focus on our custom RV pipeline for HPF, a measurement of int rinsic near-infrared RV activity in young Solar analogs, and modeling the u nderlying distribution of stellar jitter. We demonstrate on-sky stability a t the sub-2 m/s level for the K2 standard HD 3765 using a least-square s matching method to extract precise RVs. Based on a subsample of 28 stars with at least three RV measurements from our program, we find a median RMS level of 36 m/s. This is nearly a factor of 2 lower than the median RMS lev el in the optical (60 m/s) for a comparison sample with similar ages and sp ectral types as our targets. Observing in the NIR can facilitate the search for planets around young, active stars.
Danny Krolikowski, The University of Texas at Austin
Probing the formation and evolution of young planetary systems with
HPF
Sam Factor, The University of Texas at Austin
Title: TBA