Sebastien Lepine

Email:

lepineSPAMFILTER@amnh.org

Research Interests

Sebastien Lepine is a research fellow in the Astrophysics Department at the American Museum of Natural History, where he has been working since April 2000. He holds a Ph.D. in physics from the University of Montreal, where he graduated in 1998. A "cartographer of the Galaxy", he is now devoting much of his research efforts in the search for nearby stars; his goal is to obtain a most complete and accurate map of the stars located within 100 parsecs (300 light-years) of the Sun. His most notable effort is the SUPERBLINK survey, an all-sky survey of stars with large proper motions.

The nearby stars are a starting point to a wide range of research topics in astrophysics. Dr. Lepine is particularly interested in the kinematics (motions) of the nearby stars, which are used to infer the structure, dynamics, and history of our Galaxy. He is also an expert in the identification and classification of class of stars (known as "subdwarfs") which roam the Solar Neighborhood at very high speeds, are deficient in chemical elements other than hydrogen and helium, and are believed to be some of the oldest stars in our Galaxy. The nearby stars are also prime targets in the search for extra-solar planets, using both radial velocity surveys, transits (eclipses), and direct imaging techniques.

Dr. Lepine spends 30 to 40 nights per year carrying astronomical observations with various large telescopes. He is a frequent user of the 2.4-meter Hiltner and 1.3-meter McGraw-Hill telescopes ofMDM Observatory, located on the southwest ridge of Kitt Peak, 50 miles west of Tucson, AZ. Sebastien also uses the Shane 3.0-meter telescope on top of Mount Hamilton, east of San Jose CA, and part of the University of California Observatories network. He is also regularly awarded nights to use the Mayall 4-meter telescope of the Kitt Peak National Observatory.

and the Blanco 4-meter telescope at the Cerro Tololo Interamerican Observatory. Dr. Lepine also currently has observing programs using the Keck 10-meter Telescope and the Hubble Space Telescope.

Dr. Lepine's research is currently funded by grants from the National Aeronautics and Space Administration (NASA), and from the National Science Foundation (NSF).

Project Details

Mapping Stars Within 100 Parsecs of the Sun

My primary mission is to chart the nearby stars and create the most accurate 3D map of stars in the vicinity of the Sun. A complementary goal is to identify special groups of stars within that volume, including rare stars like white dwarfs, and stars which may have exoplanets. Several strategies are used to find those stars, which are hiding in images that astronomers have collected over the years. Nearby stars can be hiding "in plain sight" because it is generally not possible to measure the distances to stars from images alone, and most stars on the sky are very far away. Of the 2-3 billion stars that astronomers can detect in their images, only 300,000 are within 100 parsecs (325 light-years) of the Sun. The trick is to search for "needles in the haystack", and find which of the billions of stars are close neighbors to the Sun. The SUPERBLINK survey was developed under a grant from the National Science Foundation (NSF).

SUPERBLINK: Stars with Large Proper Motions

A big trick to find nearby stars is to watch them move. Literally. The stars in our Galaxy are not "fixed" at all, they move all over the place and travel around the Galaxy. We don't see them move only because they are very far away, though most of them travel though space at hundreds of kilometeres per second. But just like tree on the side the road seem to be zooming past us very fast when we are driving on the highway, nearby stars also appear to be moving faster than all the other stars, just because they are close to us. Our SUPERBLINK survey is a data-mining project where we try to find the 3 million stars on the sky which move the fastest. From this catalog, we expect to be able to find almost all the 300,000 stars which are within 100 parsecs of the Sun (the other stars will be a little farther away, between 100 and 400 parsecs).

The MDM-RED Spectroscopic Survey

The closer the stars, the better. Out of the 300,000 stars we have found lurking within 100 parsecs of the Sun, the most important ones are the stars in the so-called "Solar Neighborhood", or stars located within just 25 parsecs of the Sun (about 80 light-years). The stars in the Solar Neighborhood are our blood test of what kinds of stars exist in our Galaxy. Those stars are closer, so they are just easier to find. When we have them ALL, then we can calculate how many stars there are in our Galaxy per unit of space, and then estimate how many stars total there are in our Galaxy. A complete census of the nearby stars is also like a blood test of the Galaxy, telling us which types of stars exist in the Universe and what their relative numbers are. It turns out that stars like our Sun (also known as "G" stars) are relatively uncommon, while stars smaller and cooler than the Sun (also known as "red dwarfs" or "M" stars, like the star Proxima Centauri) are very abundant. We have now assembled a list which we believe contains close to 98% of all stars in the Solar Neighborhood. To figure out exactly what type of star each is, we are collecting SPECTROGRAMS of all those stars at the MDM observatory in Kitt Peak Arizona. Spectrograms have arleady been collected for about 6,000 stars, and analysis is under way. We find cool stars ("red dwarfs") to be very common indeed, as they compose over 85% of the stars in the Solar Neighborhood.

Collaborators: Kelle Cruz (Hunter College), Ian Neill Reid (Space Telescope Science Institute), Michael M. Shara (AMNH), John Thorstensen (Dartmouth College).

A Search for Nearby White Dwarfs

White dwarfs are the fading remnants of dead stars. They have stopped burning hydrogen, and shine only from their residual heat. About the size of planet Earth, they pack as much mass as the Sun. They have a very hot, bright surface, but are not very luminous because they are much smaller than regular stars; as a result, they are quite faint on the sky, and are fairly difficult to find. I have been searching for white dwarfs in the SUPERBLINK catalog of stars with large proper motions, looking for stars that are both blue and faint (which means they are hot, but are not very luminous). We are now planning to observe these stars with a spectrograph, to look for the telltale spectral signatures of white dwarfs. This program is currently supported by a grant from the National Aeronautics and Space Administration (NASA).

Collaborators: Pierre Bergeron, Marie-Michele Limoges, Alessandros Gianninas (all from Universite de Montreal)

Targets for Exoplanet Surveys: the Best Places to Search

Searching for exoplanets is a tough job, and exoplanet "hunters" don't want to lose time looking at random stars, there's just too many of them. A more efficient way is to pre-select stars around which planets are easier to detect. Nearby stars are good targets, because they are closer to the Sun and their planets will be easier to reach with our telescopes. The best ones to look for planets, however, are low-mass stars. That's because the current techniques were are now using to find planets around stars do not detect the planets themselves, but only their influence on the star. Low-mass stars are smaller, and easier to pull around: they get bullied by their planets a lot more, so it's easier to tell if they have planets. Also, our current techniques to detect work best when the planets orbit very close to their star (like Mercury around the Sun, and even closer). Low-mass stars are cool and dim, so these close planets would might still harbor life or liquid water, even if they are very close to their stars. I am now conducting a survey of low-mass stars in the Solar neighborhood, and trying to identify the very best stars to look for planets.This research effort is currently supported by a collaborative grant from the National Science Foundation (NSF).

Collaborators: Barbara Rojas-Ayala (AMNH), Matthew Wilde (AMNH), Eric Gaidos (U.Hawaii), Andrew Mann (U.Hawaii), Eric Hilton (U.Hawaii)

Publications

List of my publications at NASA's Astrophysics Data System