Assistant Professor
Department of Physics and Astronomy
California State Polytechnic University, Pomona

Research


A “Colorful” New Take on a Venerable Old Diagram

Matthew S. Povich Research Matthew S. Povich Research
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20 September 2011

Over the years I have devoted a great deal of time comparing models of young stellar objects (YSOs) to infrared (IR) spectral energy distributions (SEDs) of actual YSOs found in star-forming regions, using software tools produced by my colleague, Thomas Robitaille. YSOs have distinctive IR colors because they are surrounded by dusty, protoplanetary disks (and also accretion envelopes in the least-evolved objects). The SED analysis provides a tool for analyzing simultaneously all available measurements of colors and brightnesses for an ensemble of YSOs, and the direct comparison to models provides constraints on the underlying physical parameters for each YSO—luminosity, stellar mass, accretion rate, disk mass, and about 20 more.

Collaborator: Thomas Robitaille

 

Research Topics

 

Star Formation Rates

Matthew S. Povich Research

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Measuring the star formation rate (SFR) in the Milky Way has been a guiding theme of my research since my days as a doctoral student. The SFR, conventionally expressed as the mass of gas (in units of solar mass) converted to stars per year, is one of the most important properties of a galaxy. It would be reasonable to ask, “Haven’t we already measured this for our own Milky Way?” The answer is yes, many times, and every astronomer knows that the answer is roughly one solar mass per year. Unless it’s four...or how about two?

Collaborator: Laura Chomiuk

Paper: Chomiuk & Povich (2011)

Poster: Toward a New Calibration of Star Formation Rates in Galactic H II Regions (PDF)

Talks: A Case Study of the Galactic HII Region M17: Implications for the Galatic Star Formation Rate (PDF)The Chandra Carina Complex Project: A Spatially Resolved X-ray and Infrared Study of the Nearest Galactic Starburst Region (PDF)

 

H II Regions and Bubbles


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Wherever a young star cluster containing at least a few hundred stars forms, odds are that one (or more) of these stars will have >8 times the mass of the Sun and reach the main sequence as an O- or early B-type star. OB stars have temperatures in excess of 25,000 K and produce copious amounts of ultraviolet radiation. Ultraviolet photons with wavelengths shorter than 91.2 nm ionize hydrogen, and consequently young star clusters are often surrounded by zones of ionized hydrogen called “H II regions.”

Collaborators: Edward Churchwell, Leisa Townsley, John Bieging, Christer Watson, Robert Simpson, Chris Lintott, and the Milky Way Project Team

Papers: Churchwell et al. (2006, 2007), Povich et al. (2007, 2008, 2009), Watson et al. (2008)

Poster: On the Star Formation History of M17

Talks: Bash Symposium review talkA Case Study of the Galactic HII Region M17: Implications for the Galatic Star Formation Rate (PDF)

Press: Penn State Students Blow Bubbles in the Milky WayRivers of Gas Flow Around Stars in New Space Image

 

Massive Stars


Research of Matthew S. Povich

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The Hunt for OB stars. I would like to be able to say that, among the most massive star clusters and associations in our Milky Way Galaxy, we have a good census of the brightest, most massive stars—those with luminosities exceeding 10,000 of our Sun. Unfortunately, this is not generally the case. Exhibit A: The Great Nebula in Carina, a famous star-forming region with a rich observational history (the nebula can be seen by the naked eye from the Southern Hemisphere), containing at least 50,000 stars, of which 100 are known to be massive, O and early B-type stars. Using a combination of X-ray data from the Chandra X-ray Observatory and infrared (IR) data, I identified 94 candidate massive stars in the Carina Nebula, potentially doubling the number of massive stars in the region (Povich et al. 2011a). These results have made my research group curious to learn how many massive stars remain undiscovered in other regions, so Penn State grad student Heather Busk is searching through archival X-ray and IR data in pursuit of new candidates.

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Research of Matthew S. Povich

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Signatures of Stellar Winds. Massive stars drive extraordinarily powerful winds that reach velocities of 2,000 kilometers per second. The impact of stellar winds has been a recurring theme in my work, as evidenced by signatures including hot, X-ray-emitting plasma in giant H II regions and bow shocks associated with individual massive stars. But the wind power generated by massive stars is frustratingly difficult to measure, and different techniques can give very different answers. Lately I have been contemplating whether infrared spectral energy distribution analysis might be able to produce new, independent constraints models for the mass-loss rates (and hence the wind power) of massive stars. The idea is summarized in this cartoon figure that compares two synthetic massive star spectra, one including the effects of stellar winds and the other neglecting them. The windy spectrum produces a mid-infrared emission signature that should be measurable with broad-band photometry.

Collaborators: Leisa Townsley, Marc Gagné, Patrick Broos, Heather Busk (PSU grad student), Henry "Chip" Kobulnicky, Thomas Robitaille, M. Virginia McSwain

Papers: Povich et al. (2008, 2011a)

Talk: The Hunt for massive Stars Hiding in the Milky Way (PDF)

Press: Nearby Supernova Factory Ramps UpSpitzer Spies a 'Flying Dragon' Smoldering with Secret Star BirthRivers of Gas Flow Around Stars in New Space Image

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X-ray and Infrared Observations of Young Star Clusters and Associations

Research of Matthew S. Povich

Matthew S. Povich Research

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Penn State is home to a leading research group in X-ray studies of star-forming regions, headed by my colleagues Eric Feigelson and Leisa Townsley. I brought my NSF Fellowship to Penn State specifically to join this group and explore the power of combining infrared (IR) and X-ray data to gain a deeper understanding of young stellar populations. IR observations are relied upon to penetrate the veil of dust obscuring the youngest star clusters in visible light. But the richest star-forming regions in the Milky Way tend to be located in the Galactic plane, where IR images become dominated by older, field stars. Young stars are 100 to 1000 times more luminous in X-rays compared to field stars, hence young star clusters stand out in stark relief in X-ray images. But X-rays alone give limited information about the stars themselves, so we have come to rely on matching X-ray sources to stars observed in IR images, and then we use the IR data to derive stellar properties like luminosity, mass, presence or absence of a circumstellar disk, and so on. Many of the research results highlighted elsewhere on this site rely upon this approach.

Collaborators: Leisa Townsley, Eric Feigelson, Tim Naylor, Patrick Broos, Konstantin Getman, Robert King, Michael Kuhn (PSU grad student), Robyn Weyandt (PSU undergrad), John Bieging, Barbara Whitney, Steven Majewski, Rémy Indebetouw

Publications: Povich et al. (2011a,b)

Poster: The Chandra Carina Complex Project: Finding Oases in the X-Ray Desert of Intermediate-Mass Stars (PDF)

Talk: The Chandra Carina Complex Project: Highlights from Combined X-ray and Mid-IR Observations of the Nearest Galactic Starburst Region (PDF)

Press: New View of the Great Nebula in Carina

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Young Stellar Objects and Protoplanetary Disks


Research of Matthew S. Povich


Research of Matthew S. Povich

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Young stellar objects (YSOs) are stars that are young enough to retain their circumstellar, possibly planet-forming disks and even the remnant, accreting envelopes from their natal clouds. Radiation from the star heats the dust in these disks and envelopes, causing the dust to glow with a characteristic infrared emission signature. My colleagues Barbara Whitney and Thomas Robitaille have simulated the emission from YSOs over a wide range of physical properties, and several years ago published their first large library of YSO model spectral energy distributions (SEDs). I have fit these models to large samples of observed YSOs and tested the ability of the models to constrain the physical properties of individual YSOs and ensemble populations. The results of these explorations are published in various papers, but I will highlight some of my favorites:

  1. We have derived star formation rates in major star-forming regions, including M17 (Povich et al. 2009, Povich & Whitney 2010), the Great Nebula in Carina (Povich et al. 2011b), and the entire Large Magellanic Cloud (Whitney et al. 2008).

  2. The mass distribution of YSOs generally exhibits a deficit of high-mass sources (Figure b). This is a smoking gun for more rapid disk evolution around more massive stars (this could inhibit planet formation, although such short-lived star systems would probably not be hospitable to advanced life-forms anyway).

  3. A correlation between X-ray emission and disk mass for intermediate-mass (between 2 and 8 solar masses) YSOs suggests that X-ray emission and circumstellar disks both disappear quickly (< 1 Myr) for such stars (Povich et al. 2011b). This correlation is among the most age-sensitive observable features of rich, young stellar populations, and it raises intriguing questions about possible relationships between the stellar properties (convective versus radiative envelopes?) and disk dissipation mechanism(s) (photoevaporation versus dynamical instabilities?) for intermediate-mass stars.

Collaborators: Barbara Whitney, Thomas Robitaille, Rémy Indebetouw, Nathan Smith, Konstantin Getman, John Bieging, Wesley Orbin (PSU undergrad), Michael Alexander (U. Wyoming grad student)

Papers: Shepherd et al. (2007), Povich et al. (2009), Kang et al. (2009), Smith et al. (2010), Povich & Whitney (2010), Povich et al, (2011b)

Posters: On the Star Formation History of M17Evidence for Delayed massive Star Formation in the M17 Proto-OB Association

Talk: Intermediate-mass Young Stellar Objects: Bridging the astronomical gap between T Tauri stars and massive star formation (PDF)

Press: Spitzer Spies a 'Flying Dragon' Smoldering with Secret Star Birth

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