Kavli Affiliate: Gregory J. Herczeg
| First 5 Authors: Adolfo S. Carvalho, Adolfo S. Carvalho, , ,
| Summary:
We present the results of the first high-sensitivity NUV (1800 to 3200 AA)
survey of FU Ori objects, using the textitHubble Space Telescope (HST) STIS
spectrograph. We compare new low resolution spectra for 6 sources with
predictions from accretion disk models and find that all show emission in
excess of the disk model spectrum. The physical properties of the NUV emission
excess are very consistent among the sample, with a mean luminosity of
$10^-1.11 pm 0.4 L_odot$ and temperature of $16400 pm 2600$ K — despite
spanning 0.9 dex in $M_*$, 1.3 dex in $dotM$, and 0.7 dex in
$L_mathrmacc$. We use the spectra to conclusively rule out the existence of
a hot boundary layer in FU Ori accretion disks. We then discuss the source of
the excess emission in the context of recent simulations of FU Ori outbursts
and boundary layer accretion. The UV spectra also show the often-seen
ionC2] 2326 AA multiplet and ionMg2 2796/2803 AA doublet, as well
as the unusual ionFe2] 2507/2509 AA doublet, a feature that is not seen
in the existing UV spectra of other young stellar objects. We measure and
compare the luminosities of these lines in outbursting with those in
non-outbursting objects.
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