arXiv subjects

Karl Gordon

Publications and source records attributed to Karl Gordon.

39 records · Page 3Linked to original sources

arXiv2008

A point source survey of M31 with the Spitzer Space Telescope

We explore the stellar population of M31 in a Spitzer Space Telescope survey utilizing IRAC and MIPS observations. Red supergiants are the brightest objects seen in the infrared; they are a prominent evolutionary phase. Due to their circumstellar envelopes, many of these radiate the bulk of their luminosity at IRAC wavelengths and do not stand out in the near infrared or optically. Going fainter, we see large numbers of luminous asymptotic giant branch (AGB) stars, many of which are known long period variables. Relative to M33, the AGB carbon star population of M31 appears sparse, but this needs to be spectroscopically confirmed.

astro-ph↗

arXiv2006

M33's Variable A -- A Hypergiant Star More Than 35 Years in Eruption

Variable A in M33 is a member of a rare class of highly luminous, evolved stars near the upper luminosity boundary that show sudden and dramatic shifts in apparent temperature due to the formation of optically thick winds in high mass loss episodes. Recent optical and infrared spectroscopy and imaging reveal that its ``eruption'' begun in $\sim$1950 has ended, {\it lasting $\approx$ 45 yrs}. Our current observations show major changes in its wind from a cool, dense envelope to a much warmer state surrounded by low density gas with rare emission lines of Ca II, [Ca II] and K I. Its spectral energy distribution has unexpectedly changed, especially at the long wavelengths, with a significant decrease in its apparent flux, while the star remains optically obscured. We conclude that much of its radiation is now escaping out of our line of sight. We attribute this to the changing structure and distribution of its circumstellar ejecta corresponding to the altered state of its wind as the star recovers from a high mass loss event.

astro-ph↗

arXiv2003

SMC-Type Interstellar Dust in the Milky Way

It is well known that the sightline toward HD 204827 in the cluster Trumpler 37 shows an UV extinction curve that does not follow CCM. However, when a dust component, foreground to the cluster, is removed, the residual extinction curve is identical to that found in the SMC within the uncertainties. The curve is very steep and has little or no 2175 A bump. The position of HD 204827 in the sky is projected onto the edge of the Cepheus IRAS Bubble. In addition, HD 204827 has an IRAS bowshock indicating that it may be embedded in dust swept up by the supernova that created the IRAS Bubble. Shocks due to the supernova may have led to substantial processing of this dust. The HD 204827 cloud is dense and rich in carbon molecules. The 3.4 $μ$m feature indicating a C-H grain mantle is present in the dust toward HD 204827. The environment of the HD 204827 cloud dust may be similar to the dust associated with HD 62542 which lies on the edge of a stellar wind bubble and is also dense and rich in molecules. This sightline may be a Rosetta Stone if its environment can be related to those in the SMC having similar dust.

astro-ph↗