NOAO >   Observing Info >   Approved Programs >   2016A-0075

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Program Information for 2016A-0075


PI: Alexandros Gianninas, U. of Oklahoma, alexg@nhn.ou.edu
Address: Department of Physics and Astronomy, Room 131 Nielsen Hall, Norman, OK, 73019-0225 USA

CoI: Gilles Fontaine, University of Montreal
CoI: Mukremin Kilic, U. of Oklahoma
CoI: Warren Brown, Harvard-Smithsonian Center for Astrophysics

Title: Searching for Pulsations in Mixed Atmosphere Extremely Low-mass White Dwarfs

Abstract: We have identified three extremely low-mass (ELM) white dwarfs (WDs) with mixed atmospheres containing both hydrogen and helium. Our spectroscopic fits place these three objects outside the extended ZZ Ceti instability strip of pulsating hydrogen atmosphere WDs. Recent calculations have shown that a continuum of instability strips should exist as a function of helium abundance. Our pulsation models predict that these three ELM WDs should pulsate with periods in the range ~200-800s. Unlike the ZZ Ceti stars which display g-mode oscillations, these mixed atmosphere objects are predicted to display p-mode oscillations. Unlike g-modes, p-modes are sensitive to the composition of the core. This affords us an unprecedented opportunity to confirm that ELM WDs do in fact possess helium cores as predicted by stellar evolution. Here, we request 4 hrs of GMOS-N time to obtain time-series photometry for the two fainter (g > 19.0) candidates to confirm their nature as pulsating ELM WDs.

Program Type: Standard/Galactic

Scheduled Nights:
Run 1 (2016A):  GEM-NQ/GMOSN -- 2hrs band 2 (GN-2016A-Q-59)


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NOAO >   Observing Info >   Approved Programs >   2016A-0075

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