Infrared Spectroscopy of the FU Orionis Type Object 2MASS J06593158-0405277

ATel #6862; Bo Reipurth (IfA, Univ. Hawaii) and M. S. Connelley (IfA, Univ. Hawaii)
on 1 Jan 2015; 03:51 UT
Credential Certification: Bo Reipurth (reipurth@ifa.hawaii.edu)

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Recently Maehara, Kojima, and Fujii (ATEL #6770) announced an outburst in 2MASS J06593158-0405277 and showed its great similarity to FU Orionis using low-dispersion optical spectra. Hillenbrand (ATEL #6797) presented high dispersion optical spectra of the object, and showed that the object displays the blueshifted wings at Halpha and other lines that result from strong outflow activity characteristic of FUors. Hackstein et al. (ATEL #6838) presented archival photometry demonstrating that the outburst occurred between January and October 2014.

We have obtained a cross-dispersed near-infrared spectrum of 2MASS J06593158-0405277 with SpeX on the NASA Infrared Telescope Facility on Mauna Kea on 2014 December 20.58 UT in photometric conditions. The total on-source integration time was 960 sec and the spectral range was from 0.7 to 2.4 micron. The resolving power R is around 1300, and the signal-to-noise of the data ranges from around 50 at short wavelengths to around 450 at long wavelengths.

The spectrum is dominated by strong CO absorption bands and pronounced depressions due to water vapor, characteristic of late-type stars, the spectrum resembles those of late-K to early-M stars, although a self-consistent spectral class is difficult to assign. Such a late spectral type is completely inconsistent with the early F-type spectral class exhibited in the optical spectrum of Hillenbrand (ATEL #6797), demonstrating the well-known effect in FUors that their spectral types become gradually later with increasing wavelength. This is a result of the inner warmer disk regions dominating the optical spectrum while outer cooler disk regions dominate in the infrared (e.g., Hartmann & Kenyon 1996 [ARAA 34, 207]). The flux of the spectrum is declining towards longer wavelengths, as do K- and M- stars, and comparisons with late standard stars indicate that the FUor suffers only very slight extinction.

These results add further strength to the spectral identification of this outbursting object as a bona fide FU Orionis type eruption by Maehara, Kojima, and Fujii (ATEL #6770) and by Hillenbrand (ATEL #6797).

A K-band image covering an area of 60 by 60 arcseconds (north up and east left) was taken of 2MASS J06593158-0405277 at the IRTF at the same time as the near-infrared spectrum. The outburst source had a magnitude of 7.62 mag (the 2MASS value is K=9.45), and the image shows weak nebulosity around the source with slight substructure, this is likely a reflection nebula, indicating that the source is still associated with its nascent cloud. The image shows a 'companion' to the FUor at an angular separation of about 5.5 arcseconds at position angle 16 degrees, and with a K-band magnitude of 11.59, identified as 2MASS J06593168-0405224. The density of stars in the image is quite large, suggesting that this close-by object could be a line-of-sight association. However, the 2MASS colors of the companion indicates a substantial near-infrared excess, strongly suggesting that the object is a young star. If both stars are located at a distance between 0.5 and 1 kpc, then their projected separation would be in the range 2750 to 5500~AU.

2MASS J065931598-0405277 is located towards a small cloud of low extinction, which we identify as Lynds 1650 (aka TGU 1535 and Dobashi 5011; Dobashi et al. 2005 [PASJ 57, SP1], Dobashi 2011 [PASJ 63, SP1]).

SpeX spectrum: http://www.ifa.hawaii.edu/users/reipurth/PREPRINTS/fig1.png

K-band image: http://www.ifa.hawaii.edu/users/reipurth/PREPRINTS/fig2.png