An Ultraviolet Spectrum of the Tidal Disruption Flare ASASSN-14li
  We present a Hubble Space Telescope STIS spectrum of ASASSN-14li, the first
rest-frame UV spectrum of a tidal disruption flare (TDF). The underlying
continuum is well fit by a blackbody with $T_{\mathrm{UV}} = 3.5 \times 10^{4}$
K, an order of magnitude smaller than the temperature inferred from X-ray
spectra (and significantly more precise than previous efforts based on optical
and near-UV photometry). Super-imposed on this blue continuum, we detect three
classes of features: narrow absorption from the Milky Way (probably a
high-velocity cloud), and narrow absorption and broad (FWHM $\approx 2000$-8000
km s$^{-1}$) emission lines at/near the systemic host velocity. The absorption
lines are blueshifted with respect to the emission lines by $\Delta v =
-(250$-400) km s$^{-1}$. Due both to this velocity offset and the lack of
common low-ionization features (Mg II, Fe II), we argue these arise from the
same absorbing material responsible for the low-velocity outflow discovered at
X-ray wavelengths. The broad nuclear emission lines display a remarkable
abundance pattern: N III], N IV], He II are quite prominent, while the common
quasar emission lines of C III] and Mg II are weak or entirely absent. Detailed
modeling of this spectrum will help elucidate fundamental questions regarding
the nature of the emission process(es) at work in TDFs, while future UV
spectroscopy of ASASSN-14li would help to confirm (or refute) the previously
proposed connection between TDFs and "N-rich" quasars.
