Variability of the FU Ori-type object V900 Mon at thermal wavelengths

ATel #8174; W. P. Varricatt, T. H. Kerr, T. Carroll, E. Moore (United Kingdom Infrared Telescope, Hawaii)
on 16 Oct 2015; 03:01 UT
Credential Certification: Watson Varricatt (w.varricatt@ukirt.hawaii.edu)

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V900 Mon (2MASS 06572222-0823176) was discovered as an eruptive variable by Thommes et al. (2011, CBET #2795). Based on the spectral line features observed, they suggested a FU Ori type for this object. Multi-wavelength observational study by Reipurth et al. (2012, 748, L5) confirmed a FU Ori type; they proposed a Class I protostar with a massive envelope and found that the brightening of the source was slow rather a sudden.

We obtained imaging photometric observations of this source on three epochs, using the 3.8-m United Kingdom Infrared Telescope (UKIRT), and The UKIRT 1-5 micron Imager Spectrometer (UIST) with the L' and M' MKO filters, at a pixel scale of 0.12"/pixel. The table below shows the details of our observations and the magnitudes derived. A 4"-diameter software aperture was used for photometry. The magnitudes are in the UKIRT photometric system.

 
------------------------------------------------------- 
UTDate   | UT     | Heliocentric |Filter|   V900 Mon 
yyyymmdd | hrs    | Julian Date  |      | mag.  | error 
         |        | 2457000 +    |      |       | 
------------------------------------------------------- 
20150426 |5.7785  | 138.73917    | L'   | 5.905 | 0.025 
20150427 |5.8010  | 139.74003    | L'   | 5.886 | 0.025 
20150905 |15.0654 | 271.12495    | L'   | 5.835 | 0.025 
 
20150426 |5.8680  | 138.74290    | M'   | 5.300 | 0.020 
20150427 |5.9661  | 139.74691    | M'   | 5.275 | 0.020 
20150905 |15.1654 | 271.12910    | M'   | 5.248 | 0.020 
------------------------------------------------------- 

Reipurth et al. obtained an L' magnitude of 6.44 ± 0.09 (in a 4.8"-diameter aperture) from their observations on UT 20100102; the L' magnitude obtained by us on UT 20150905 is 0.6 mag brighter. The L' photometric standard used (HD40335) was the same in both studies. We used a smaller aperture (4" diameter) for deriving the magnitudes, but increasing the aperture to 4.8" in our photometry makes the object brighter only by 0.01 mag in L'

During the period of our observations, we see a brightening of 0.07 mag and 0.05 mag in L' and M', respectively. We are continuing the monitoring of this source.

The UKIRT is supported by NASA, and operated under an agreement among the University of Hawaii, the University of Arizona, and Lockheed Martin Advanced Technology Center; the operations are enabled through the cooperation of the East Asian Observatory.