Physics
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30180f&link_type=abstract
Spitzer Proposal ID #30180
Physics
Scientific paper
We are proposing to invest a small amount of Spitzer/IRS time to acquire a low resolution spectrum from 5.2-38 microns as part of a program to ascertain the physical nature of a 24-micron bright/IRAC faint enigmatic object seen in the direction of the LMC. This object just discovered while investigating the infrared SED of gravitational microlensing event MACHO-LMC-4, as a part of GTO program PID 118 "Macho Search". We serendipitously noted an object in both the IRAC and MIPS fields-of-view that was very bright at 24 microns (9 mJy), but had very low flux levels in all IRAC bandpasses (0.93 mJy at 8 microns). Because of the shape of the broadband SED as observed by IRAC and MIPS, we favor two basic possibilities as being the most likely explanation for the nature of his object: (1) A z~2 starburst galaxy, where the strong 24 micron emission is produced by 8 micron rest-frame PAH emission redshifted into the MIPS 24 micron bandpass or (2) A dust enshrouded luminous blue variable (LBV) in a pre-planetary nebula (pre-PN) evolutionary state. We will use the IRS in standard staring mode to acquire spectra with both low resolution modules in the range of 5.2 - 38 microns. A IRS low-resolution spectrum will reveal a more detailed picture of the shape of its SED. We estimate that no more than 1 hour will be required to obtain spectra with sufficient signal-to-noise to determine whether this object is a distant starburst galaxy (via a PAH emission peak) or a more nearby pre-PN LBV (a rising continuum that flattens off towards the mid-IR). The proposed observation represents the first stage of investigating nature of this object.
Ashby Matthew
Barmby Pauline
Fazio Giovanni
Hora Joseph
Kallivayalil Nitya
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