HV 11423: The Coolest Supergiant in the SMC

Abstract

We call attention to the fact that one of the brightest red supergiants in the SMC has recently changed its spectral type from K0-1 I (December 2004) to M4 I (December 2005) and back to K0-1 I (September 2006). An archival spectrum from the Very Large Telescope reveals that the star was even cooler (M4.5-M5 I) in December 2001. By contrast, the star was observed to be an M0 I in both October 1978 and October 1979. The M4-5 I spectral types is by far the latest type seen for an SMC supergiant, and its temperature in that state places it well beyond the Hayashi limit into a region of the H-R diagram where the star should not be in hydrostatic equilibrium. The star is variable by nearly 2 mag in V, but essentially constant in K. Our modeling of its spectral energy distribution shows that the visual extinction has varied during this time, but that the star has remained essentially constant in bolometric luminosity. We suggest that the star is currently undergoing a period of intense instability, with its effective temperature changing from 4300 K to 3300 K on the time-scale of months. It has one of the highest 12-micron fluxes of any RSG in the SMC, and we suggest that the variability at V is due primarily to changes in effective temperature, and secondly, due to changes in the local extinction due to creation and dissipation of circumstellar dust. We speculate that the star may be nearing the end of its life.

Accepted by the Astrophysical Journal

References in corpus (3)

• The Effective Temperatures and Physical Properties of Magellanic Cloud Red Supergiants: The Effects of Metallicity
• Variability in red supergiant stars: pulsations, long secondary periods and convection noise
• Bringing VY Canis Majoris Down to Size: An Improved Determination of Its Effective Tempeature

Cited by in corpus (33)

• Surveying the Agents of Galaxy Evolution in the Tidally-Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC) II. Cool Evolved Stars
• The temperatures of Red Supergiants
• Radiative hydrodynamics simulations of red supergiant stars: I. interpretation of interferometric observations
• Radiative hydrodynamics simulations of red supergiant stars. IV gray versus non-gray opacities
• Red Supergiants in the Andromeda Galaxy (M31)
• Late-Type Red Supergiants: Too Cool for the Magellanic Clouds?
• Betelgeuse Just Isn't That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse
• The Period-Luminosity Relation of Red Supergiant Stars in the Small Magellanic Cloud
• Spitzer Infrared Spectrographic point source classification in the Small Magellanic Cloud
• A serendipitous survey for variability amongst the massive stellar population of Westerlund 1
• Spectral Types of Red Supergiants in NGC 6822 and the Wolf-Lundmark-Melotte Galaxy
• The Physical Properties of the Red Supergiant WOH G64: The Largest Star Known?
• Massive Stars in the Galaxies of the Local Group
• The Time-Averaged Mass-Loss Rates of Red Supergiants As Revealed by their Luminosity Functions in M31 and M33
• Red supergiant stars in the Large Magellanic Cloud. II. Infrared properties and mid-infrared variability
• Physical Properties of Red Supergiants
• Evolved Massive Stars at Low-metallicity II. Red Supergiant Stars in the Small Magellanic Cloud
• The Ionized Nebula surrounding the Red Supergiant W26 in Westerlund 1
• The Optical to Infrared Extinction Law of Magellanic Clouds Based on Red Supergiant and Classical Cepheid
• Identification of dusty massive stars in star-forming dwarf irregular galaxies in the Local Group with mid-IR photometry
• A dearth of OH/IR stars in the Small Magellanic Cloud
• Physical parameters of red supergiants in dwarf irregular galaxies in the Local Group
• The Infrared Massive Stellar Content of M83
• Revisiting the progenitor of the low-luminosity type II-plateau supernova, SN 2008bk
• Investigating episodic mass loss in evolved massive stars: II. Physical properties of red supergiants at subsolar metallicity
• Asymptotic Giant Branch Stars in the Nearby Dwarf Galaxy Leo P
• The Physical Properties of Red Supergiants: Comparing Theory and Observations
• Red Supergiants in the Local Group
• Massive stars in their death-throes
• Red Supergiants -- The Other Side of the H-R Diagram
• Red Supergiants in the Milky Way and Nearby Galaxies
• The Red Supergiant Content of the Local Group
• Testing Evolutionary Models with Red Supergiant and Wolf-Rayet Populations