astro seminar

Estimating Stellar Atmospheric Parameters for the MaStar Stellar Library

Stellar parameter determination represents a critical step in the procedure of Simple Stellar Population Synthesis (SSPS), of which the aim is to produce realistic composite spectra for model stellar populations, such as galaxies and star clusters. As SDSS-IV nears completion, the MaStar stellar library, an unprecedented large and comprehensive collection of medium-resolution stellar spectra from ~10,000 unique stars, will be made available to the public in its entirety. In order to make proper use of such a library in SSPS, accurate stellar parameter estimates (Teff, log g, [Fe/H], and [\alpha/Fe]) associated with the spectra are a necessity. Here, I present a new approach to stellar parameter estimation that we in the MaStar team have developed in recent years, which combines the spirit of conventional methods with the goal of obtaining an efficient and versatile software pipeline for delivering stellar parameter estimates, as well as other important data such as extinction estimates. This method makes use of the continuum-normalized stellar spectra and the spectral continua themselves (often characterized by photometric measurements in previous efforts) to match the MaStar spectra to models derived from the ATLAS9-based BOSZ model set via reduced-\chi^2 fitting. Carefully combining these two approaches allows us to avoid many of the problems that afflict each approach separately, and obtain reliable estimates throughout parameter space, including notoriously difficult regimes, such as at higher temperatures (> 7000 K). Steps are also taken to account for extinction and flux calibration residuals present in the data. Since this project is ongoing, focus will be placed on recent progress, preliminary results, and plans for the near future.
Date: 
Thursday, April 30, 2020 - 4:00pm to 5:00pm
Location: 
https://uky.zoom.us/j/94381145379?status=success
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Hui Li

Date: 
Thursday, March 26, 2020 - 4:00pm to 5:00pm
Location: 
BL 339
Type of Event (for grouping events):

A New Mask for An Old Suspect -- Testing the Sensitivity of the Galactic Center Excess to the Point Source Mask

The Galactic center excess has lingered as a possible, but ambiguous, signal of new physics for several years. It has previously been argued that certain details of the excess emission imply that it likely originates from a population of point sources, but this remains a topic of vigorous debate. In this talk, I will report on my recent work, relying on a new point source catalog (obtained by the Fermi-LAT collaboration), that sheds light on this controversial topic. After giving some background on the excess, I will discuss various metrics that have been used to try to understand its true nature. I will show that the large majority of bright sources that were previously suggested to be members of the excess are indeed contained in the new Fermi-LAT point source catalog -- and yet, despite masking out these sources (so that they cannot contribute to the excess), the excess remains just as bright in our new fit to the data. I will go on to discuss the implications of our findings for the two most popular interpretations of the excess.

Date: 
Thursday, December 19, 2019 - 4:00pm to 5:00pm
Location: 
BL 339
Type of Event (for grouping events):

Jet Dynamics and Feedback: Deep X-ray Observations of Centaurus A and M87

Date: 
Thursday, October 31, 2019 - 4:00pm to 5:00pm
Location: 
BL 339
Type of Event (for grouping events):

Astro Seminar: A Post-Mortem on Post-Starburst Galaxies

While much effort has been expended to detect the earliest galaxies and to follow their evolution to z~0, astronomers remain baffled by the present-day dichotomy between disky, star forming (aka late-type) galaxies and quiescent, spheroidal (aka early-type) galaxies. Finding galaxies in transition from one class to the other, whose spectra indicate intense recent star formation that has now ended, is key.  We have identified thousands of such "post-starburst galaxies" and discovered that they are often the products of late-type galaxy-galaxy mergers. Their current kinematics, stellar populations, and morphologies are consistent with late- to early-type galaxy evolution. I will discuss recent work that further demonstrates the importance of these galaxies in the study of galaxy evolution. In particular, we have shown that their molecular gas fractions decline rapidly in time after the starburst ends and in a manner consistent with feedback processes. Furthermore, we have determined that tidal disruption events, in which a star is disrupted by the supermassive black hole in a galaxy's center, favor post-starburst galaxies by factors of tens to hundreds. Like the well-known black hole-bulge mass correlation, this surprising connection between the properties of a galaxy on kpc scales and its supermassive black hole on pc scales requires explanation. 
 
Date: 
Thursday, October 19, 2017 - 4:00pm to 5:00pm
Location: 
CP 179
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Astro Seminar: Magnetic Fields and Star Formation: An Observational Perspective

Star formation is one of the fundamental processes of
astrophysics. Yet in spite of much progress in recent years,
many of the elements of the physics governing star formation remain uncertain,
including the role played by magnetic fields. Depending on their strengths, magnetic fields may strongly affect the formation and evolution of dense molecular clouds from which stars form, and appear to be essential in transferring angular momentum outward so that protostars and planets may form. This talk will describe the observational techniques that are available to study the role of magnetic fields in star formation regions, review the current state of the observational results, and briefly discuss possible future developments.
Date: 
Thursday, September 17, 2015 - 4:00pm to 5:00pm
Location: 
CP171
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Astro Seminar: Mapping Ten Thousand Nearby Galaxies in 3D

Mapping Nearby Galaxies at APO (MaNGA) is an ongoing integral field spectroscopy survey carried out as part of the Sloan Digital Sky Survey-IV.
Started in the fall of 2014, MaNGA is utilizing multiple hexagonal fiber bundles fed to the BOSS spectrograph on the 2.5m Sloan Telescope to study the internal structure and formation history of roughly 10,000 nearby galaxies
spanning a wide range in mass, type, and environment. Fiber bundles of various diameters ranging from 12 arcsec to 32 arcsec are used to match the apparent size distribution of galaxies. Most target galaxies will be covered out to 1.5-2.5 effective radii with a spatial resolution of 1-2kpc. Such spatially resolved spectroscopy beyond the central fibers covered by previous
generation of SDSS can provide a great deal of information about each galaxy. I will give an overview of science goals of the survey, discuss the hardware design, survey sample design, observing strategy, and the data quality of MaNGA.
I will also showcase some interesting examples from the 1400 galaxies we have already observed.
Date: 
Thursday, September 10, 2015 - 4:00pm to 5:00pm
Location: 
CP171
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