absTracTs
Dust
in high Galactic latitude cirrus
Blagrave,
K. P. M.
Using our series of GBT high latitude H I maps (9.2
arcmin resolution), we
investigate variations of near-IR dust emissivities over more than 700
square
degrees. It is found that in a number of circumstances, the data
require two
emissivities: one for the local gas and one for the intermediate
velocity gas.
This poster will present a statistical analysis of our derived
distribution of
emissivities and discuss what this might imply about the dust
properties in
our variety of high-latitude fields.
The
dust-gas correlation of Intermediate Velocity Clouds at the North
Ecliptic Pole
Blagrave,
K. P. M., and Martin, P. G.
Surveys of H I emission reveal the presence of high
Galactic latitude H I gas at velocities inconsistent with Galactic
rotation:
intermediate-velocity clouds and high-velocity clouds. To constrain the
connection of these clouds to the local gas,
we have been involved in an on-going project to correlate H I and
infrared emission.
Deviations
from He I Case B Recombination Theory and Extinction Corrections in the
Orion Nebula
Blagrave,
K. P. M.; Martin, P. G.; Rubin, R. H.; Dufour, R. J.; Baldwin, J. A.;
Hester, J. J.; Walter, D. K.
We are engaged in a comprehensive program to find
reliable elemental
abundances in and probe the physical structure of the Orion Nebula, the
brightest
and best-resolved H II region. In the course of developing a robust
extinction correction
covering our optical and UV FOS and STIS observations, we examined the
decrement
within various series of He I lines. The decrements of the 23S-n3P,
23P-n3S, and 33S-n3P
series are not in accord with case B recombination theory. None of
these anomalous He I
decrements can be explained by extinction, indicating the presence of
additional radiative
transfer effects in He I lines ranging from the near-IR to the near-UV.
CLOUDY
photoionization equilibrium models including radiative transfer are
developed
to predict the observed He I decrements, and the quantitative agreement
is quite
remarkable. Following from these results, select He I lines are
combined with H I
and [O II] lines and stellar extinction data to validate a new
normalizable analytic
expression for the wavelength dependence of the extinction. In so
doing, the He+/H+
abundance is also derived.
A
photoionized Herbig-Haro object in the Orion nebula
Blagrave, K. P. M.;
Martin, P. G.; Baldwin, J. A.
The spectra of Herbig Haro objects are usually
characteristic of ionization
and excitation in shock-heated gas,
whether an internal shock in an unsteady outflow or a bow shock
interface with the interstellar medium. We examine the eastern-most
shock -- the leading optically visible shock -- of a Herbig Haro
outflow (HH 529) seen projected on the face of the Orion nebula, using
deep
optical echelle spectroscopy, showing that the spectrum of this gas is
consistent with photoionization by θ1 Ori C. By
modeling the
emission lines, we determine a gas-phase abundance of Fe which is
consistent with the
depleted (relative to solar) abundance found in the Orion nebula --
evidence
for the presence of dust in the nebula and therefore in the Herbig Haro
outflow. The spectrum also allows for the calculation of temperature
fluctuations, t2, in the nebula and the shock.
These fluctuations have been used to explain discrepancies between
abundances obtained from recombination
lines versus those obtained from collisionally-excited lines, although
to date
there has not been a robust theory for how such large fluctuations (t2
> 0.02) can exist.
On
the O II ground
configuration energy levels
Blagrave, K. P. M.;
Martin, P. G.
The most accurate way to measure
the energy levels for the O II
2p3 ground configuration has been from the
forbidden lines
in
planetary nebulae. We present an analysis of modern planetary nebula
data that nicely constrain the splitting within the 2D
term
and the separation of this term from the ground 4S3/2
level. We extend this method to H II
regions
using high-resolution spectroscopy of the Orion nebula, covering all
six
visible transitions within the ground configuration. These data confirm
the splitting of the 2D term while additionally
constraining
the splitting of the 2P term. The energies of
the 2P and 2D terms
relative to the ground
(4S) term are constrained by requiring that all
six lines
give the same radial velocity, consistent with independent limits
placed
on the motion of the O+ gas and the planetary
nebula data.
Temperature
variations from HST Spectroscopy of the Orion nebula
Rubin, R. H.;
Martin, P. G.; Dufour, R. J.;
Ferland, G. J.;
Blagrave, K. P. M.;
Liu, X.-W.; Nguyen, J. F.;
Baldwin, J. A.
We present Hubble Space Telescope (HST)/STIS
long-slit spectroscopy of
NGC 1976. Our goal is to measure the intrinsic line ratio [OIII]
4364/5008 and thereby evaluate the electron temperature (Te)
and the fractional mean-square Te variation
(t2A)across the nebula.
We also measure the
intrinsic line ratio [NII] 5756/6585 in order to estimate Te
and t2A in the N+
region. The
interpretation of the [NII] data is not as clear cut as the [OIII] data
because of a higher sensitivity to knowledge of the electron density as
well as a possible contribution to the [NII] 5756 emission by
recombination (and cascading). We present results from binning the data
along the various slits into tiles that are 0.5 arcsec square (matching
the slit width). The average [OIII] temperature for our four HST/STIS
slits varies from 7678 K to 8358 K; t2A
varies
from 0.00682 to at most 0.0176. For our preferred solution, the average
[NII] temperature for each of the four slits varies from 9133 to 10232
K; t2A varies from
0.00584 to 0.0175. The
measurements of Te reported here are an average
along each
line of sight. Therefore, despite finding remarkably low
t2A, we cannot rule out
significantly larger
temperature fluctuations along the line of sight. The result that the
average [NII]Te exceeds the average [OIII]Te
confirms what has been previously found for Orion and what is expected
on theoretical grounds. Observations of the proplyd P159-350 indicate:
large local extinction associated; ionization stratification consistent
with external ionization by θ1 Ori C; and
indirectly,
evidence of high electron density.
Line-of-sight
optical emission in the Orion nebula
Blagrave, K. P. M., Baldwin, J. A., and Martin, P. G.
The Orion nebula is
as near-ideal a region as one can find
in which
to study the content, structure, and dynamics of the interstellar
medium in
star-forming regions because of both its proximity and its high surface
brightness.
Deep optical echelle spectra were obtained for three different
lines-of-sight
using the Blanco 4m telescope at the Cerro Tololo Inter-American
Observatory
(CTIO). This poster discusses the velocity and ionization structure
inferred
from the identification of approximately 300 permitted and forbidden
lines
along each of the three lines-of-sight including a discussion of the
different mechanisms responsible for exciting the lines.
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