Investigating the 43 Helium core white dwarfs candidates in NGC 6752
By: Ricardo Flores
Department: Astronomy
Faculty Advisor: Dr. Adrienne Cool
I report on a study of 43 intriguing stars in the globular star cluster NGC 6752. These stars had previously been identified as white dwarfs possibly composed of helium. White dwarfs are the burned-out remnants of stars, the vast majority of which are composed of carbon and oxygen. The much more rare helium white dwarfs are generally found only in the presence of binary companions. We have carried out a detailed visual inspection of these 43 stars using Hubble Space Telescope images taken in three different filters (blue, red, and Hydrogen-alpha). We find that a significant fraction of the stars fall within or near Airy patterns of luminous nearby stars. In a rating system that we developed (1-4, with 1 meaning that a star is isolated from any neighbors, and 4 meaning that a star lies within the Airy pattern of brighter neighboring star), 12 stars were rated "1", 6 stars were rated "2", 11 stars were rated "3" and 14 stars were rated "4". Given the relatively high fraction of stars rated 3 and 4 [25] vs. stars rated 1 or 2 [18], our next step will be a statistical analysis to assess whether the helium white dwarfs are over-represented in very crowded regions. If so, this will suggest that a portion of the candidates could be the result of the difficulty of obtaining accurate measurements in regions of extreme stellar crowding and enable us to correct for this in our assessment of the total population of helium white dwarfs in NGC 6752.