* Astronomy

Title: Spitzer Observations of Var Her 04: Possible Detection of Dust Formation in a Super-Outbursting TOAD
Authors: David R. Ciardi, Stefanie Wachter, D. W. Hoard, Steve B. Howell, Gerard T. van Belle

Researchers present four MIPS (24 µm) and two IRAC (3.6, 4.5, 5.8, and 8.0 µm) Spitzer observations of the newly discovered Tremendous Outburst Amplitude Dwarf nova (TOAD) Var Her 04 during decline from super-outburst. The four MIPS observations span 271 days and the two IRAC observations span 211 days. Along the line-of-sight to Var Her 04, there is a foreground M-star within 1 arcsec of the variable; as a result, all of the Spitzer photometry presented in this paper is a blend of the foreground M-star and Var Her 04.
They estimate the quiescent level of the TOAD to be ΔV=4-5 magnitudes below that of the M-star. Based upon the spectral energy distribution and the 2MASS colours, they find the M-star to be an M3.5V dwarf at a distance of 80-130 pc. Based upon its outburst amplitude and quiescent apparent magnitude, the researchers estimate the distance to Var Her 04 to be 200-400 pc, suggesting that the line-of-sight foreground star is physically unrelated to the cataclysmic variable.
All of the Spitzer photometry is consistent with the photospheric emission of the line-of-sight M3.5V star, except for one 24 µm observation obtained after the variable re-brightened. This 24 µm flux density is 75 µJy (4\sigma) above the preceding and following MIPS observations. The researchers tentatively suggest that the mid-infrared brightening of 75 µJy may be associated with a dust formation event in the super-outburst ejecta. Assuming a dust temperature of 100-400 K, they have estimated the amount of dust required. They find 10^-13 - 10^-11 solar masses of dust is needed, consistent with amounts of mass ejection in TOADs expected during super-outburst, and possibly making TOADs important contributors to the recycling of the interstellar medium.

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