Massive star population of the Virgo Cluster galaxy NGC4535

Discovery of new massive variable candidates with the Hubble Space Telescope^⋆

¹ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
e-mail: zspetsieri@noa.gr
² Department of Astrophysics, Astronomy & Mechanics, Faculty of Physics, University of Athens, 15783 Athens, Greece
³ Czech Academy of Sciences, Astronomical Institute, Fricova 298, 251 65 Ondrejov, Czech Republic
⁴ Laboratoire AIM, CEA/IRFU/Service d’Astrophysique, Université Paris Diderot, Bat. 709, 91191 Gif-sur-Yvette, France
⁵ IESL/FORTH & University of Crete, Greece
⁶ INAF Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Naples, Italy
⁷ Space Telescope Science Institute, 3700 San Martin Drive, 21218 Baltimore, MD, USA
⁸ ESA, SRE Operations Division, Spain
⁹ Sternberg Astronomical Institute, Moscow State University, Universitetskii pr. 13, 119992 Moscow, Russia
¹⁰ Astro Space Center of Lebedev Physical Institute, Profsoyuznaya Str. 84/32, 117997 Moscow, Russia

Received: 24 April 2018
Accepted: 20 July 2018

Abstract

We analyzed the massive star population of the Virgo Cluster galaxy NGC 4535 using archival Hubble Space Telescope Wide Field Planetary Camera 2 images in filters F555W and F814W, equivalent to Johnson V and Kron-Cousins I. We performed high precision point spread function fitting photometry of 24353 sources including 3762 candidate blue supergiants, 841 candidate yellow supergiants, and 370 candidate red supergiants. We estimated the ratio of blue to red supergiants as a decreasing function of galactocentric radius. Using Modules for Experiments in Stellar Astrophysics (MESA) isochrones at solar metallicity, we defined the luminosity function and estimated the star formation history of the galaxy over the last 60 Myr. We conducted a variability search in the V and I filters using three variability indexes: the median absolute deviation, the interquartile range, and the inverse von-Neumann ratio. This analysis yielded 120 new variable candidates with absolute magnitudes ranging from M_V = −4 to −11 mag. We used the MESA evolutionary tracks at solar metallicity to classify the variables based on their absolute magnitude and their position on the color-magnitude diagram. Among the new candidate variable sources are eight candidate variable red supergiants, three candidate variable yellow supergiants and one candidate luminous blue variable, which we suggest for follow-up observations.