August 2015

The Bridge Program’s Growing Influence in Tennessee

The 2015-2016 start of the Bridge Program ushers in a new era of Bridge Program! Through a successful collaborative program between Tennessee State University (TSU) and Vanderbilt this year marks the expansion of the Tennessee-wide Louis Stokes Alliance for Minority Participation (LSAMP) to include students of the Fisk-Vanderbilt Master’s-to-PhD Bridge Program.

To read more about these excifing changes and the role the Bridge Program played, head over to the Article at Diverse Issues in Higher Education.

April 2015

TSU, Vanderbilt win nearly $1 million to increase minority STEM Ph.D.s

This news release was written by Melanie Moran and originally published in Vanderbilt Research News. Link to original article.

2012 graduates of the Fisk-Vanderbilt-Master’s-to-Ph.D. Bridge Program (Vanderbilt University)
2012 graduates of the Fisk-Vanderbilt-Master’s-to-Ph.D. Bridge Program (Vanderbilt University)

Increasing the number of minority students who earn a Ph.D. in science, technology, engineering and math is the aim of a new “bridge to doctorate” program being launched by a coalition of Tennessee universities and led by Tennessee State University and Vanderbilt University.

“We are thrilled to be working with TSU and our other Tennessee partners on this project. We all benefit by increasing the number of underrepresented minority students earning their Ph.D.s in these fields,”Art Overholser, senior associate dean of the Vanderbilt School of Engineering and co-director of the new program, said. “The perspectives and talents of the students we hope to attract will not only enrich our research and teaching of STEM disciplines, but will serve as an example and inspiration for students to come.”

The National Science Foundation recently awarded $987,000 to TSU to launch the new program as an expansion of the Tennessee Louis Stokes Alliance for Minority Participation, or TLSAMP. TLSAMP is a NSF-funded collaborative effort by 10 Tennessee colleges and universities to significantly increase and improve the retention of underrepresented minority students in STEM fields statewide. TLSAMP is led by TSU and includes Fisk University, LeMoyne-Owen College, Middle Tennessee State UniversityNashville State Community CollegeSouthwest Tennessee Community CollegeTennessee Technological University, University of Memphis, University of Tennessee – Knoxville and Vanderbilt.

“We are delighted that Vanderbilt University is the inaugural host for the Tennessee Bridge-to-the–Doctorate program. One of our goals is to increase the number of students attending graduate school. This award allows more of our students to transition into such programs,” Lonnie Sharpe, Massie Chair of Excellence at Tennessee State University and TLSAMP executive director, said. “I am excited about this great opportunity for our students to continue their quest for doctoral degrees in science, technology, engineering and mathematics.”

The new program, tagged TLSAMP BD @ VU, will fund 12 students and will recruit students both nationally and within TLSAMP institutions. Students must complete undergraduate degrees in science, technology, engineering and mathematics fields to qualify for the program.

TLSAMP BD @ VU will build upon the success and lessons learned from the Fisk-Vanderbilt Masters-to-Ph.D. Program. Launched in 2004, the two-year program has built a detailed, research-based toolkit to support underrepresented minority students’ on their path to earning a Ph.D.

Rather than selecting students based on the usual metrics of test scores or grade point averages alone, the bridge program looks at how the students display “grit” and how they tackle academic challenges. Students are given a clear road map of what they will need to do to apply to and be admitted to a Ph.D. program, and work closely every step of the way with a mentor on their studies and collaborative research projects. Mentors are trained to identify possible trouble points and to step in quickly to help students stay on track, and also connect the students to the broader scientific community.

As a result of that program, Vanderbilt has become the leading producer of underrepresented minority Ph.D.s in astronomy, materials science and physics. Since its launch in 2004, the program has graduated 16 Ph.D.’s, all of whom have gone on to careers in academia, industry and national laboratories. The new funding will allow this model to be expanded across all STEM disciplines and will involve every STEM Ph.D. program at Vanderbilt.

“We have built a robust and nationally visible platform through the Fisk-Vanderbilt Bridge Program for underrepresented minority Ph.D.s in the sciences. Now with this NSF Bridge to the Doctorate grant, we have the opportunity to scale up and make an impact in engineering also,” Keivan Stassun, professor of physics and astronomy at Vanderbilt and co-director of TLSAMP BD @ VU, said. “Importantly, this also represents an experiment to reform STEM graduate education that will further position TLSAMP partner institutions as leaders in at last solving the so-called ‘diversity pipeline problem’ in STEM.”

Mark Hardy, vice president for academic affairs at TSU, is the principal investigator on the TLSAMP BD @ VU grant and will be assisted on the project by Sharpe. Dina Stroud, research assistant professor in clinical pharmacology, is the executive director of TLSAMP BD @ Vanderbilt.

This news release was written by Melanie Moran and originally published in Vanderbilt Research News. Link to original article.

June 2014

Grit better than GRE for predicting grad student success

This article was written by David Salisbury and published in Vanderbilt Research News. Link to original article.

Selecting graduate students in the fields of science and engineering based on an assessment of their character instead of relying almost entirely on their scores on a standardized test would significantly improve the quality of the students that are admitted students and, at the same time, boost the participation of women and minorities in these key disciplines.

That is the argument made in the essay “A test that fails,” published in the June 12 issue of the journal Nature. The authors are Casey Miller, associate professor of physics at the University of South Florida, and Keivan Stassun, professor of physics and astronomy at Vanderbilt University and Fisk University, who are both involved in successful bridge programs designed to improve Ph.D. completion rates among all students and to boost women and underrepresented minority participation in the fields of science, technology, engineering and math (STEM).

According to the authors, the primary reason that half of all American Ph.D. students fail to graduate, and the primary barrier holding back women and minority students, is American academia’s over-reliance on the GRE, the graduate record examination, a standardized test introduced in 1949 that most U.S. graduate schools require for admission. The problem is that the exam’s quantitative score – the part measuring math ability – is not a good predictor of a student’s ultimate success, particularly in the STEM fields. Women, on average, score 80 points lower in the physical sciences than men, and African Americans score 200 points below whites. At the same time, studies performed by ETS, the company that administers the test, have found that the test’s predictive ability is limited to first-year graduate course grades and even that is questionable in STEM fields.

“In simple terms, the GRE is a better indicator of sex and skin color than of ability and ultimate success,” the article states.

Despite its demonstrable demographic bias, graduate-admissions committees routinely use minimum GRE scores to filter applications. A typical procedure is to reject the application of any candidate scoring less than 700 on the 800-point quantitative section, despite the fact that this practice violates ETS guidelines.

“The misuse of GRE scores to select applicants may be a strong driver of the continuing under-representation of women and minorities in graduate school. Indeed, women earn hardly 20 percent of U.S. physical sciences Ph.D.s and underrepresented minorities – who account for 33 percent of US university-age population – earn just 6 percent. These percentages are striking in their similarity to the percentage of students who score above 700 on the GRE Quantitative Measure,” the article points out.

Miller and Stassun propose an alternative approach to the selection process, which has proven successful in the bridge programs with which they are involved: Using a 30 minute face-to-face interview that examines an individual’s college and research experiences, key relationships, leadership experience, service to the community, and life goals. This provides committee members with a good indication not only of the person’s academic training and aptitude but also of the other competencies that point to a likelihood of success in graduate school and a STEM career.

The validation for this approach is the track record of the students in their programs. At the Fisk-Vanderbilt bridge program, for example, 85 percent of the students would have been eliminated by the 700-point GRE cutoff. However, 81 percent of the 67 students who have entered the program – including 56 underrepresented minorities and 35 women – have earned, or are making good progress toward their Ph.D.s and all the students who have received their doctorates have found employment in the STEM workforce, as post doctoral students, university faculty members or staff scientists in national labs or industry. This 81 percent success rate is significantly better than the 50 percent national average, which most policy makers agree is an enormous waste of precious human resources.

Keivan Stassun, center right, with Fisk-Vanderbilt Ph.D. Bridge Program students. (Daniel Dubois / Vanderbilt)

Miller and Stassun make it clear that they are not advocating the admission of unqualified minorities in the name of social good. Instead, they argue that the nation can swell the ranks of its STEM workforce – a goal that is broadly agreed upon by policy makers to improve the nation’s international competitiveness – by adopting a more accurate graduate school admission process that improves the quality of admitted Ph.D. students and that doesn’t eliminate large numbers of talented minority and women students who have the right stuff to succeed in these challenging careers.

This article was written by David Salisbury and published in Vanderbilt Research News. Link to original article.

May 2014

Astronomers identify signature of Earth-eating stars

This article was written by David Salisbury and originally published in Vanderbilt Research News. Link to original article.

Some Sun-like stars are ‘Earth-eaters.’ During their development they ingest large amounts of the rocky material from which ‘terrestrial’ planets like Earth, Mars and Venus are made.

Trey Mack, a graduate student in astronomy at Vanderbilt University, has developed a model that estimates the effect that such a diet has on a star’s chemical composition and has used it to analyze a pair of twin stars that both have their own planets.

The results of the study were published online May 7 in the Astrophysical Journal.

“Trey has shown that we can actually model the chemical signature of a star in detail, element by element, and determine how that signature is changed by the ingestion of Earth-like planets,” said Vanderbilt Professor of Astronomy Keivan Stassun, who supervised the study. “After obtaining a high-resolution spectrum for a given star, we can actually detect that signature in detail, element by element.”

This ability will add substantially to astronomers’ understanding of the process of planet formation as well as assist in the ongoing search for Earth-like exoplanets, according to the astronomers.

First, some background: Stars consist of more than 98 percent hydrogen and helium. All the other elements make up less than 2 percent of their mass. Astronomers have arbitrarily defined all the elements heavier than hydrogen and helium as metals and have coined the term “metallicity” to refer to the ratio of the relative abundance of iron to hydrogen in a star’s chemical makeup.

Since the mid-1990’s, when astronomers developed the capability to detect extrasolar planets in large numbers, there have been several studies that attempt to link star metallicity with planet formation. In one such study, researchers at Los Alamos National Laboratory argued that stars with high metallicity are more likely to develop planetary systems than those with low metallicity. Another study concluded that hot Jupiter-sized planets are found predominantly circling stars with high metallicity while smaller planets are found circling stars with a wide range of metal content.

Trey Mack. (Steve Green - Vanderbilt)
Trey Mack. (Steve Green – Vanderbilt)

Building on the work of coauthor Simon Schuler of the University of Tampa, who expanded the examination of stars’ chemical composition beyond their iron content, Mack took this type of analysis a step further by looking at the abundance of 15 specific elements relative to that of the Sun. He was particularly interested in elements like aluminum, silicon, calcium and iron that have melting points higher than 1,200 degrees Fahrenheit (600 degrees Celsius) because these are the refractory materials that serve as building blocks for Earth-like planets.

Mack, Schuler and Stassun decided to apply this technique to the planet-hosting binary pair designated HD 20781 and HD 20782. Both stars should have condensed out of the same cloud of dust and gas and so both should have started with the same chemical compositions. This particular binary pair is the first one discovered where both stars have planets of their own.

Both of the stars in the binary pair are G-class dwarf stars similar to the Sun. One star is orbited closely by two Neptune-size planets. The other possesses a single Jupiter-size planet that follows a highly eccentric orbit. The difference in their planetary systems make the two stars ideal for studying the connection between exoplanets and the chemical composition of their stellar hosts.

When they analyzed the spectrum of the two stars the astronomers found that the relative abundance of the refractory elements was significantly higher than that of the Sun. They also found that the higher the melting temperature of a particular element, the higher was its abundance, a trend that serves as a compelling signature of the ingestion of Earth-like rocky material. They calculated that each of the twins would have had to consume an additional 10-20 Earth-masses of rocky material to produce the chemical signatures. Specifically, the star with the Jupiter-sized planet appears to have swallowed an extra ten Earth masses while the star with the two Neptune-sized planets scarfed down an additional 20.

The results support the proposition that a star’s chemical composition and the nature of its planetary system are linked.

Solar Spectrum
What if we could determine if a given star is likely to host a planetary system like our own by breaking down its light into a single high-resolution spectrum and analyzing it? A spectrum taken of the Sun is shown above. The dark bands result from specific chemical elements in the star’s outer layer, like hydrogen or iron, absorbing specific frequencies of light. By carefully measuring the width of each dark band, astronomers can determine just how much hydrogen, iron, calcium and other elements are present in a distant star. The new model suggests that a G-class star with levels of refractory elements like aluminum, silicon and iron significantly higher than those in the Sun may not have any Earth-like planets because it has swallowed them. (N.A.Sharp, NOAO/NSO/Kitt Peak FTS/AURA/NSF)

“Imagine that the star originally formed rocky planets like Earth. Further, imagine that it also formed gas giant planets like Jupiter,” said Mack. “The rocky planets form in the region close to the star where it is hot and the gas giants form in the outer part of the planetary system where it is cold. However, once the gas giants are fully formed, they begin to migrate inward and, as they do, their gravity begins to pull and tug on the inner rocky planets.

“With the right amount of pulling and tugging, a gas giant can easily force a rocky planet to plunge into the star. If enough rocky planets fall into the star, they will stamp it with a particular chemical signature that we can detect.”

Following this logic, it is unlikely that either of the binary twins possesses terrestrial planets. At one twin, the two Neptune-sized planets are orbiting the star quite closely, at one-third the distance between the Earth and the Sun. At the other twin, the Jupiter-sized planet spends a lot of time in the outer reaches of the planetary system but it’s eccentric orbit also brings It in extremely close to the star. The astronomers speculate that the reason the star with the two Neptune-size planets ingested more terrestrial material than its twin was because the two planets were more efficient at pushing material into their star than the single Jupiter-sized planet was at pushing material into its star.

Keivan Stassun. (Daniel Dubois / Vanderbilt)
Keivan Stassun. (Daniel Dubois / Vanderbilt)

If the chemical signature of G-class stars that swallow rocky planets proves to be universal, “when we find stars with similar chemical signatures, we will be able to conclude that their planetary systems must be very different from our own and that they most likely lack inner rocky planets,” said Mack. “And when we find stars that lack these signatures, then they are good candidates for hosting planetary systems similar to our own.”

Added Stassun: “This work reveals that the question of whether and how stars form planets is actually the wrong thing to ask. The real question seems to be how many of the planets that a star makes avoid the fate of being eaten by their parent star?”

The research was supported by National Science Foundation grants AAG AST-1009810 and PAARE AST-0849736.

This article was written by David Salisbury and originally published in Vanderbilt Research News. Link to original article.

January 2014

Surprising new class of “hypervelocity stars” discovered escaping the galaxy

This article was written by David Salisbury and published in Vanderbilt Research News. Link to original article.

Rogue Stars
Top and side views of the Milky Way galaxy show the location of four of the new class of hypervelocity stars. These are sun-like stars that are moving at speeds of more than a million miles per hour relative to the galaxy: fast enough to escape its gravitational grasp. The general directions from which the stars have come are shown by the colored bands. (Graphic design by Julie Turner, Vanderbilt University. Top view courtesy of the National Aeronautics and Space Administration. Side view courtesy of the European Southern Observatory.)

An international team of astronomers has discovered a surprising new class of “hypervelocity stars” – solitary stars moving fast enough to escape the gravitational grasp of the Milky Way galaxy.

The discovery of this new set of “hypervelocity” stars was described at the annual meeting of the American Astronomical Society this week in Washington, D.C., and is published in the Jan. 1 issue of the Astrophysical Journal.

“These new hypervelocity stars are very different from the ones that have been discovered previously,” said Vanderbilt University graduate student Lauren Palladino, lead author on the study. “The original hypervelocity stars are large blue stars and appear to have originated from the galactic center. Our new stars are relatively small – about the size of the sun – and the surprising part is that none of them appear to come from the galactic core.”

The discovery came as Palladino, working under the supervision of Kelly Holley-Bockelmann, assistant professor of astronomy at Vanderbilt, was mapping the Milky Way by calculating the orbits of Sun-like stars in the Sloan Digital Sky Survey, a massive census of the stars and galaxies in a region covering nearly one quarter of the sky.

“It’s very hard to kick a star out of the galaxy,” said Holley-Bockelmann. “The most commonly accepted mechanism for doing so involves interacting with the supermassive black hole at the galactic core. That means when you trace the star back to its birthplace, it comes from the center of our galaxy. None of these hypervelocity stars come from the center, which implies that there is an unexpected new class of hypervelocity star, one with a different ejection mechanism.”

Kelly and Lauren
Lauren Palladino, right, and Kelly Holley-Bockelmann. (John Russell / Vanderbilt)

Astrophysicists calculate that a star must get a million-plus mile-per-hour kick relative to the motion of the galaxy to reach escape velocity. They also estimate that the Milky Way’s central black hole has a mass equivalent to four million suns, large enough to produce a gravitational force strong enough to accelerate stars to hyper velocities. The typical scenario involves a binary pair of stars that get caught in the black hole’s grip. As one of the stars spirals in toward the black hole, its companion is flung outward at a tremendous velocity. So far, 18 giant blue hypervelocity stars have been found that could have been produced by such a mechanism.

Now Palladino and her colleagues have discovered an additional 20 sun-sized stars that they characterize as possible hypervelocity stars. “One caveat concerns the known errors in measuring stellar motions,” she said. “To get the speed of a star, you have to measure the position really accurately over decades. If the position is measured badly a few times over that long time interval, it can seem to move a lot faster than it really does. We did several statistical tests to increase the accuracy of our estimates. So we think that, although some of our candidates may be flukes, the majority are real.”

The astronomers are following up with additional observations.

The new rogues appear to have the same composition as normal disk stars, so the astronomers do not think that their birthplace was in the galaxy’s central bulge, the halo that surrounds it, or in some other exotic place outside the galaxy.

The big question is: what boosted these stars up to such extreme velocities? We are working on that now,” said Holley-Bockelmann.

Katharine Schlesinger from the Australian National University, Carlos Allende Prieto from the Universidad de La Laguna in Spain, Timothy Beers from the National Optical Astronomy Observatory in Tucson, Young Sun Lee from New Mexico State University and Donald Schneider from Pennsylvania State University also contributed to the discovery.

The research was supported by funds from the Graduate Assistance in Areas of National Need program, National Science Foundation grants AST 0847696, AST 0607482, Physics Frontier Center grants PHY 0216783, the Aspen Center for Physics, the Alfred P. Sloan Foundation and the U.S. Department of Energy Office of Science.

August 2013

A brighter method for measuring the surface gravity of distant stars

This article was written by David Salisbury and published in Vanderbilt Research News. Link to original article.

Astronomers have found a clever new way to slice and dice the flickering light from a distant star in a way that reveals the strength of gravity at its surface.

That is important because a star’s surface gravity is one of the key properties that astronomers use to calculate a star’s physical properties and assess its evolutionary state.

The new technique can also be used to significantly improve estimates of the sizes of the hundreds of exoplanets that have been discovered in the last 20 years. Current estimates have uncertainties ranging from 50 percent to 200 percent. Using the improved figures for the surface gravity of the host stars calculated by the new method should cut these uncertainties at least in half.

Keivan Stassun. (Daniel Dubois / Vanderbilt)
Keivan Stassun. (Daniel Dubois / Vanderbilt)

The technique was developed by a team of astronomers headed by Vanderbilt Professor of Physics and Astronomy Keivan Stassun and is described in the Aug. 22 issue of the journal Nature.

“Once you know a star’s surface gravity then you only need one other measurement, its temperature, which is pretty easy to obtain, to determine its mass, size and other important physical properties,” said Stassun.

“Measuring stellar surface gravities well has always been a difficult business,” added Gibor Basri, professor of astronomy at the University of California, Berkeley who contributed to the study. “So it is a very pleasant surprise to find that the subtle flickering of a star’s light provides a relatively easy way to do it.”

Measuring stellar gravity

There are three traditional methods for estimating a star’s surface gravity: photometric, spectroscopic and asteroseismic. The new flicker method is simpler than the older methods and more accurate than all but one of them.

Photometric methods look at how bright a star is in different colors. This distribution is linked to its surface gravity, temperature and chemical composition. It is a relatively easy observation to make and can be performed even on fairly faint stars, but does not produce a very accurate figure for surface gravity, having an uncertainty range of 90 to 150 percent.

Star granulation simulations
Simulations of granulation patterns on the surface of the Sun, sub-giant and giant stars. The scale of each simulation is proportional to the size of the blue image of earth next to it. (Courtesy of R. Trampedach, JILA/CU Boulder, CO)

The spectroscopic technique is more involved and is limited to relatively bright stars, but it has a lower uncertainty range of 25 to 50 percent. It works by closely examining the narrow spectral bands of light emitted by the elements in the star’s atmosphere. Generally speaking, high surface gravity widens the lines and lower surface gravity narrows them.

Asteroseismology is the gold standard, with accuracies of a few percent, but the measurements are even more difficult to make than spectroscopy and it is restricted to several hundred of the closest, brightest stars. The technique traces sound pulses that travel through the interior of a star at specific frequencies that are tied to its surface gravities. Small stars, like the sun, ring at a higher pitch while giant stars ring a lower pitch.

Much like asteroseismology, the new flicker method looks at variations in the star’s brightness, In this case it zeroes in on variations that last eight hours or less. These variations appear to be linked to granulation, the network of small cells that cover the surface of a star that are caused by columns of gas rising from the interior. On stars with high surface gravity, the granulation is finer and flickers at a higher frequency. On stars with low surface gravity, the granulation is coarser and they flicker at a lower frequency.

Exquisitely simple

The new method is remarkably simple – requiring only five lines of computer code to make the basic measurement – substantially reducing the cost and effort required to calculate the surface gravities of thousands of stars.

“The spectroscopic methods are like surgery. The analysis is meticulous and involved and very fine-grained,” said Stassun. “Flicker is more like ultrasound. You just run the probe around the surface and you see what you need to see. But its diagnostic power – at least for the purpose of measuring gravity – is as good if not better.”

To determine the accuracy of the flicker method, they used it to calculate the surface gravity of stars that have been analyzed using asteroseismology. They found that it has an uncertainty of less than 25 percent, which is better than both the photometric and spectroscopic methods. Its major limitation is that it requires extremely high quality data taken over long time periods. But this is precisely the type of observations made by Kepler while it was searching for periodic dips in light caused when exoplanets cross the face of a star. So the Flicker method can be applied to the tens of thousands of stars already being monitored by Kepler.

“The exquisite precision of the data from Kepler allows us to monitor the churning and waves on the surfaces of stars,” said team member Joshua Pepper, assistant professor of physics at Lehigh University. “This behavior causes subtle changes to a star’s brightness on the time scale of a few hours and tells us in great detail how far along these stars are in their evolutionary lifetimes.”

Playing with data yields discovery

Graduate student Fabienne Bastien was responsible for discovering that valuable information was embedded in starlight flicker. The discovery began when she was “playing around” with Kepler data using special data visualization software that Vanderbilt astronomers have developed for investigating large, multi-dimensional astronomy datasets. (The data visualization tool that enabled this discovery, called Filtergraph, is free to the public.)

Fabienne Bastien (Steve Green / Vanderbilt)
Fabienne Bastien (Steve Green / Vanderbilt)

“I was plotting various parameters looking for something that correlated with the strength of stars’ magnetic fields,” said Bastien. “I didn’t find it, but I did find an interesting correlation between certain flicker patterns and stellar gravity.”

When Bastien showed her discovery to Stassun, he was intrigued. So they performed the operation on the archived Kepler light curves of a few hundred sun-like stars.

When they plotted the overall variation in brightness of stars against their flicker intensity, they found an interesting pattern. As stars age, their overall variation falls gradually to a minimum. This is easily understood because the rate at which a star spins decreases gradually over time. As stars approach this minimum, their flicker begins to grow in complexity – a characteristic that the astronomers have labeled “crackle.” Once they reach this point, which they call the flicker floor, the stars appear to maintain this low level of variability for the rest of their lives, though it does appear to grow again as the stars approach the ends of their lives as red giant stars.

“This is an interesting new way to look at stellar evolution and a way to put our Sun’s future evolution into a grander perspective,” said Stassun.

When they ran their analysis on the sun’s light curve, for example, the researchers found that it is hovering just above the flicker floor, leading them to the prediction that the sun is approaching a time when it will undergo a fundamental transition to a state of minimum variability and, in the process, will lose its spots.

The research was funded by the Vanderbilt Initiative in Data-intensive Astrophysics (VIDA) and National Science Foundation grants AST-0849736 and AST-1009810.

This article was written by David Salisbury and published in Vanderbilt Research News. Link to original article.

May 2013

Vanderbilt’s role in new planet-finding space mission

This article was written by David Salisbury and published in Vanderbilt Research News. Link to original article.

exoplanet transit
Artist conception of exoplanet transiting the face of distant star. (Courtesy of MIT/Kavli Institute for Astrophysics and Space Research)

A team of Vanderbilt astronomers headed by Keivan Stassun will play a key role in the planet-seeking space telescope that NASA has just approved and scheduled for launch in 2017.

The $200 million spacecraft is called the Transiting Exoplanet Survey Satellite (TESS). When it is launched in 2017, TESS will perform the first space-borne all-sky survey for planets circling the brightest stars.

The project is headed by scientists at MIT’s Kavli Institute for Astrophysics and Space Research. Stassun is a co-principal investigator on the project and he and his team will be selecting the specific stars that the project will target in its search for subtle, periodic dips in brightness that occurs when a planet transits across a star’s face.

Artist concept of the TESS spacecraft. (Courtesy of MIT’s Kavli Institute for Astrophysics and Space Research)

“I got involved in 2011 during a sabbatical at MIT,” said Stassun, who is a professor of physics and astronomy at Vanderbilt. “At the time, one of the issues they were struggling with was how to select the most promising stars to search for planets.”

It was a process he had already worked through for KELT, the Kilodegree Extremely Little Telescope: a pair of small, land-based telescopes built and operated by Vanderbilt and Ohio State University that are designed specifically for identifying bright stars with planets. KELT, as will TESS, simultaneously records the light coming from millions of the brightest stars and so faces a similar selection problem. “I was able to tell them that we’ve already addressed the problem. They liked our approach so they invited us to join the mission,” he added.

When it is launched TESS will complement the observations being made by Kepler, NASA’s first mission capable of finding Earth-sized planets around other stars. Kepler was designed to observe much fainter stars than TESS but it is focused on a relatively small portion of the Milky Way galaxy. Three Vanderbilt astronomers, including Stassun, are also members of the Kepler science team. As of last January, Kepler had identified 2,740 candidate planets, which are steadily being confirmed by follow-up observations from other telescopes.

Most of the exoplanets that have been discovered to date are giant planets, like Jupiter. Kepler has discovered a number of smaller exoplanets, closer to the size of Earth. But Kepler has difficulty identifying smaller planets because the stars that it examines tend to be extremely faint, which makes it very difficult to confirm discoveries with ground-based telescopes. TESS, by contrast, is targeting the brightest stars specifically to make it easier to discover Earth-sized planets.

“We will be targeting mainly G-type stars similar to the Sun,” said Stassun. “Not only should concentrating on the brightest stars make it easier to find Earth-like planets, but, once we have found them, it should be possible to use large land-based telescopes to get spectra of the planet’s atmosphere.”

TESS target stars
Chart shows the stars that TESS will be targeting in red and those currently being targeted by the Kepler space telescope in blue. (Courtesy of MIT’s Kavli Institute for Astrophysics and Space Research.)

These spectra are important because they could provide information about the chemical make-up of the planetary atmospheres. If certain chemicals, like oxygen and methane, are detected it would be a strong indicator that a planet is capable of supporting life.

“We will also target a small number of red dwarf stars (such as Barnard’s star which was discovered by Vanderbilt’s first astronomer) because these are the stars nearest to us. If we are to imagine ever traveling to visit another world, it will be a world around one of these red dwarf neighbors,” Stassun said.

February 2013

Stassun on Producing Minority Ph.D. Recipients: How Vanderbilt Became the Nation’s Top Producer of Minority Ph.D. Recipients in Physics, Astronomy and Materials Science

This article was originally published in Vanderbilt News. Link to original article.

Keivan Stassun, physics and astronomy professor (DANIEL DUBOIS)
Keivan Stassun, physics and astronomy professor (DANIEL DUBOIS)

Not long after he arrived at Vanderbilt nine years ago, Keivan Stassun, professor of astronomy, began building on a newly forged alliance with Fisk University, a historically black college just two miles from the Vanderbilt campus, in an effort to increase the number of African Americans, Latinos, Native Americans and other minorities earning Ph.D. degrees in science. Since 2004 the Fisk–Vanderbilt Master’s-to-Ph.D. Bridge program, which he directs, has admitted more than 60 students. This year it will become the nation’s No. 1 producer of minority Ph.D. recipients in physics, astronomy and materials science. Students typically receive two years’ training in the master’s program at Fisk before entering Ph.D. programs at Vanderbilt or another institution.

How did the Fisk–Vanderbilt Bridge program come about?

When I was choosing among offers from several universities, I asked about opportunities and resources for doing world-class research. I also asked about opportunities and resources for really tackling what has been a century-long problem: the full inclusion of all Americans in science and engineering. Vanderbilt was the only place that gave what I considered a satisfactory answer—that they would back me as I worked to build something that would help put Vanderbilt in a leadership position nationally in tackling the challenge of diversity in higher education. That says a lot to energetic young scholars and has helped us attract the best junior faculty looking for a place to build a life centered on unique and visionary work.

Why did you opt for the Fisk partnership?

We knew other institutions had tried and failed to build partnerships that were merely handoffs, not true collaborations that would ensure students were adequately trained. One of the first questions we considered was in which areas of research we could legitimately build a student training program. Fisk has a world-class research program in a number of science and engineering areas, including nanophysics, the development of novel materials for space-based astrophysics, infrared spectroscopy of molecules, and synthesis of those molecules for materials science applications. That allowed us to build a collaboration wherein Vanderbilt astrophysicists like myself and Fisk nanophysicists such as bridge program co-director Arnold Burger could work together to develop cutting-edge detector technology for use in the next generation of space exploration. It gives us something specific around which to train students, and it allows us to compete for grants.

What makes the program attractive to students?

One of the most important things we have done for these students is to give them, in essence, the opportunity to audition in person. We know that, by and large, the students we are trying to attract often underperform on metrics like the Graduate Record Examination (GRE). A key insight for us was to get past the focus on standardized tests as the be-all and end-all. If the student has been working in your lab for two years, making discoveries alongside you, and taking hard graduate-level courses from you and publishing in peer-reviewed journals, then maybe we don’t need the GRE. We replaced a predictor of performance with actual performance. That has been one of the great innovations of our bridge program, and it’s the reason Columbia and MIT and Michigan are now emulating it. For decades the top-tier Ph.D.-granting institutions have wanted to make headway on the challenge of diversity at the Ph.D. level, and now they have our example to follow. It’s nice to be emulated.

Considering the amount of time this must require of faculty members, has it been difficult to enlist their involvement?

A serious commitment to training and mentoring certainly takes time, but it’s an investment that contributes to research productivity. These students contribute directly to discoveries in my lab. My faculty colleagues—especially David Ernst, Kelly Holley-Bockelmann, Donna Webb and David Cliffel—have found ways to make sure students are integrally connected with the mission of the university to discover and advance knowledge. If we want America to remain globally competitive, we must do a better job of tapping our own talent. And doing the right thing raises the bottom line across multiple measures of performance. We now have at least seven Vanderbilt faculty members who were able to be more competitive and ultimately win National Science Foundation CAREER Award grants—the top national award for junior science faculty—in part because they were able to demonstrate in their NSF proposals their involvement with this program.

Why is it so important to attract more minority students to science in particular?

Science, engineering and technology in the U.S. depend absolutely on the size and quality of the talent pool. Historically, we have not effectively drawn from what is now a third of our population. Fewer than half of our African American youth will graduate from high school, let alone be in a position to consider pursuing a Ph.D. In running a master’s-to-Ph.D. program that links Fisk and Vanderbilt, we have tried to articulate one very specific part of a larger system where we can exert leverage. I hope and I pray that the better angels among us continue to tackle those other very hard parts of the pipeline, because we must.

June 2012

Bridging the Gap in the Sciences

Vanderbilt is on track this year to become the number one producer of minority Ph.D. recipients in physics, astronomy and materials science, an area where minorities are grossly underrepresented. Watch the emotional journey of the latest doctoral graduates from the Fisk-Vanderbilt-Master’s-to-Ph.D. Bridge Program.

February 2010

Astronomer receives NSF award to study black hole evolution

This article was originally written and published by the Vanderbilt View staff. Link to original article.

Kelly Holley-Bockelmann
Kelly Holley-Bockelmann

Holley-Bockelmann will receive $1.1 million over five years

Kelly Holley-Bockelmann, assistant professor of physics and astronomy, has been awarded the National Science Foundation’s largest-ever Faculty Early Career Development grant in the field of astronomy. She will use the award to continue her studies of black holes while supporting Vanderbilt’s innovative program designed to make the university the top producer of underrepresented minorities with Ph.D.s in physics and astronomy.

Due to the availability of Recovery Act funds, Holley-Bockelmann will receive $1.1 million over five years. CAREER awards are considered NSF’s most prestigious honor for junior faculty members.

Holley-Bockelmann plans to address one of the fundamental mysteries that surrounds supermassive black holes, exotic objects weighing in at millions to billions of solar masses which astronomers have found lurking at the core of most galaxies, including the Milky Way.

Understanding how supermassive black holes form is important because they have played a major role in the evolution of the universe. Specifically, they appear to have had a major impact on the development of galaxies in ways such as affecting the rate at which they produce new stars.

Holley-Bockelmann also will use part of her grant to support the Fisk-Vanderbilt Master’s-to-Ph.D. Bridge Program, a partnership with historically black Fisk University designed to encourage underrepresented minorities and women to pursue careers in physics and other sciences. She is following in the footsteps of Vanderbilt Associate Professor of Physics and Astronomy Keivan Stassun, who received a CAREER Award in 2004 and used it to start the Bridge program.

“As a first-generation college student and a woman astronomer, it’s important for me to help students realize that they can be a scientist no matter where they come from or what they look like, as long as they love science enough to put in the hard work,” Holley-Bockelmann said.

Holley-Bockelmann, who is an adjunct professor at Fisk, will hire two Bridge graduates to assist in her black hole studies. Her grant is also providing “time release” for a Fisk instructor to finish up his doctoral degree. In addition, she is hiring a post-doctoral fellow to assist in her black hole studies and a graduate student to serve as a computational guru for the Bridge program.

This article was originally written and published by the Vanderbilt View staff. Link to original article.