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Pupin 1327

marcel at

+1 212 854 6814

+1 212 854 8121

MC 5246
550 W120th St
NY NY 10027

CU astronomy »

I am an observational astronomer who is interested in using new datasets and technologies to address classic questions in stellar astrophysics. One example is the survey of open clusters I am leading to calibrate the relationship between stellar age, rotation, and magnetic activity. The existence of such a relationship was established 45 years ago in solar-mass stars, but its exact form and theoretical underpinnings remain unknown, especially in stars less massive than the Sun. This has implications for stellar evolution and for observationally determining the ages of field stars, an exercise that currently is surprisingly frustrating.

To calibrate the relationship between rotation and age, I have relied on photometric data from automated, wide-area surveys like those conducted by the Palomar Transient Factory (PTF) and the repurposed Kepler mission, K2. Surveys like these have revolutionized our ability to measure these periods systematically in nearby open clusters, and over the past few years my group has obtained PTF and K2 periods for hundreds of stars in the Hyades, Praesepe, and Pleiades, among others.

To examine the relationship between age and activity, I target these same clusters with a number of observatories, including Columbia's very own (well, co-own) MDM Observatory, as well as the Chandra X-ray Observatory, Swift Gamma-Ray Burst Mission, and XMM-Newton. Optical spectra from MDM and elsewhere, and X-ray data from Chandra, Swift, and XMM can constrain how magnetic heating impacts stellar chromospheres and coronae. By combining these data with PTF and Kepler periods, I hope to clarify the interplay between a star's angular momentum and its magnetic field, and how the two evolve over time in low-mass stars.

I also study white dwarfs and neutron stars, two of the possible endpoints of stellar evolution. In these stars fusion has ended and degeneracy pressure is preventing gravitational collapse. White dwarfs are typically the size of the Earth but two-thirds as massive as the Sun, while neutron stars, city-sized but roughly one and a half times the mass of the Sun, are even more compact. In particular, I am interested in observationally constraining the mass-radius relationship for neutron stars, and in using binary white dwarfs to determine the relationship between a star's main sequence mass and the mass of the white dwarf it will form when it dies (the initial-to-final mass relation). Here I rely heavily on data from the Sloan Digital Sky Survey, and occasionally on access to the 3.5 m at Apache Point Observatory.

I use targeted observations at wavelengths ranging from X-rays to the infrared and large-scale survey data, both photometric and spectroscopic. (You can check my ADS publications for more details.) Using these data has unexpected consequences, like having an asteroid named after me... and even more amazingly, my work has earned me Columbia's Distinguished Faculty Award and a Presidential Early Career Award for Scientists and Engineers.