Transcript spie_poster1 - University of Maryland

First Observations of Extended Objects with
UVES/VLT: h Carinae, the Discovery of the Ghost
Shell, and the Strontium Filaments
D. G. Currie (Physics Dept., University of Maryland & European Southern Observatory, Garching bei Muenchen, Germany)
B. N. Dorland (Physics Dept., University of Maryland & Astrometry Dept., U.S. Naval Observatory, Washington DC)
A. Kaufer (European Southern Observatory, Santiago, Chile)
ABSTRACT
The Ultraviolet and Visible Echelle Spectrograph (UVES) on the European Southern Observatory's Very Large Telescope (VLT) has
been used to observe the extended nebular features surrounding h Carinae. We discuss the UVES instrument and our observations
of h Carinae, that is, the discovery of the "Ghost Shell" and investigation of the Strontium Filaments (SrF). These are the first
published results on extended objects using UVES.
VLT Unit 4 during assembly
Paranal observatory
location in Chile’s
Atacama desert offers
some of the driest
conditions in the
southern hemisphere.
The Very Large Telescope/Ultraviolet and
Visible Echelle Spectrograph
h Carinae: Background
Carina
Nebula
The UVES Instrument on the VLT, with a spectral resolution of ~100,000, a collecting aperture of 8.2 meters and a
wide spectral coverage from the UV atmospheric cutoff to 1 micron, is one of the most powerful systems to
investigate the dynamics, physical and chemical properties of extended objects like supernova remnants,
planetary nebula and h Carinae. We describe it's general properties and capabilities.
One of the most massive stars in the galaxy, h Carinae is also
one of the most enigmatic. It is thought to be an extreme
member of the “Luminous Blue Variable” (LBV) class of
evolved stars. According to the historical record, prior to
1842, its magnitude varied about +3 +/- 1 mv. In 1842, it
experienced a cataclysmic eruption that temporarily
increased its magnitude to -1, making it one of the brightest
stars in the sky. This “Great Eruption” resulted in, among
other things, the creation of the “Homunculus”, a
circumstellar nebula consisting of dust and gas ejected
during the eruption.
UVES is a two-arm cross-dispersed Echelle spectrograph covering the wavelength range 300 - 500 nm (blue) and 420 - 1100 nm (red). The spectral
resolution for a 1 arcsec slit is about 40,000. The maximum resolution that can be attained with still adequate sampling, using a narrow slit, is about
110,000 in the red and 80,000 in the blue. The dioptric cameras offer fields with a diameter of 43.5 mm (blue) and 87 mm (red) and have external focal
planes for easy detector interfacing and upgrading during the life of the instrument. The baseline CCD detector is a 2k x 4k, 15 µm pixel size thinned,
back-illuminated EEV chip. Each arm has two cross-disperser gratings; the order separation is 12 arcsec minimum. The spectrum can be scanned on
the CCDs in both directions.
Auxiliary devices include calibration lamps, an iodine absorption cell for high precision radial velocity studies, image slicers, depolarizer, image derotator, ADC and filter wheels. On-line information on the object position and the energy passed by the slits is provided by technical CCD slit viewers
and exposure meters. A recent addition is a fiber port for 8 fibers (e.g. 6 objects, 2 sky) feeding the red arm. With fibers of 1 arcsec diameter, this
facility will provide the possibility to perform multi-object cross-dispersed Echelle spectroscopy with R ~ 40,000 in the spectral range 420 - 1100 nm.
The fiber inputs are located on the multifiber positioner at the other Nasmyth focus of UT2. The instrument components are placed inside a passive
enclosure which provides thermal isolation from the environment. The control and CCD electronics are located in temperature controlled cabinets
outside the enclosure. All functions are permanently on-board and remotely selectable without manual intervention.
After 1842, its brightness dropped to mv = +8; slowly
brightening in the intervening years to about +5.5 today.
During this post Great Eruption phase, it has demonstrated
continued variability, including a “Lesser Eruption” in 1890,
and 5.52 year variability cycle that has been observed in Xray, UV, Visible, IR and RF portions of the frequency
spectrum.
UVES Observational Capabilities
Parameter
Blue
Red
Wavelength range
300 - 500 nm
420 - 1100 nm
Resolution-slit product
41,400 arcsec
38,700 arcsec
~80,000
~110,000
18.7 at R = 55,000 in U
20.3 at R = 55,000 in V
18.7 at R = 90 000 in V
6 % at 320 nm
15 % at 470 nm
18 % at 500 nm
9 % at 900 nm (with EEV chip)
Camera
dioptric F/1.8, 70 µm/arcsec
field 43.5 mm diam.
dioptric F/2.5, 97 µm/arcsec
field 87 mm diam.
CCDs and pixel scale
2K x 4K, EEV 15 µm pixels
(0.22 arcsec/pix)
mosaic of two 2K x 4K, EEV 15
µm pixels
(0.16 arcsec/pix)
Echelle
41.59 g/mm, R4 mosaic
31.6 g/mm, R4 mosaic
Cross dispersers (g/mm and
blaze)
#1: 1200 g/mm, 330 nm
#2: 660 g/mm, 420 nm
#3: 600 g/mm, 510 nm
#4: 316 g/mm, 770 nm
80 nm in 30 orders
200 nm in 45 orders
12 arcsec or 50 pixels
12 arcsec or 75 pixels
Max. resolution
Limiting magnitude
(3hr, S/N~10, median seeing)
Overall detective quantum
efficiency (DQE) (from top of the
telescope, wide slit)
Typical wavelength range/frame
Order separation (minimum)
VLT Spectral Coverage
1842 “Great Eruption”
1890 “Lesser
Eruption”
h Carinae and the Homunculus
observed from Hubble Space Telescope.
UVES instrument layout (l.) and 3-D CAD depiction (r.)
(with instrument cover removed)
h Carinae’s historical light curve.
h Carinae’s “Ghost Shell”
h Carinae’s Strontium Filaments
The Ghost Shell is an emission nebula outside the Homunculus discovered by the authors in 2002 using UVES data. It
is apparently a shock wave propagating at about 1000 km/sec. The properties of the feature are a critical test of the
theories of high-velocity shock wave, lying in a relatively unexplored domain between the adiabatic shocks of young
supernova remnants and the radiative shock of stellar jets. Explanation of the Ghost Shell model will necessitate
additional observations and extension of the current models into this new regime.
-850 km/sec
-800 km/sec
-750 km/sec
The “Strontium Filament” is a bright linear feature, first observed in HST/STIS data by Zethson, Gull and Hartman,
that appears to have been ejected from the central star ~100 years ago. The “Linear Filament” extends ~ 4
arcsec NW of the central star, and is quite narrow. It is characterized by emission lines from numerous heavy
metal species, including Vanadium, Scandium, Titanium and Strontium that are absent elsewhere in the nebula.
The strontium detection is especially interesting, as it has never been detected in emission before h Carinae.
-150
-100
-50
0
[Fe I] (7 lines)
4”
Curved
Filament
-700 km/sec
-650 km/sec
CF1
-600 km/sec
CF2
Linear
Filament
UVES long slit observations of h Carinae used to
discover and analyze the Ghost Shell feature. “AOS”
indicates Homunculus axis of symmetry.
LF2
1”
-150
Line of sight
d = ~2.2 kpc
-50
CF2
Axis of Symmetry
i = 40 deg
Ghost
Shell
(continuous)
-100
Fe I (16 lines)
NW
lobe
~17 arcsec
~37 kAU
~200 light-days
~0.2 pc
LF3
CF1
LF2
SE
lobe
5”
Plane of the Sky
-100
-50
0
0”
-150
Ghost
Shell
(disrupted)
Derived velocity data for Ghost Shell feature for multiple emission
species. Velocities are along slit -7 (r.) and axis of symmetry (l.) (i.e.,
between slits).
2”
UVES Channeled spectra for the Ghost Shell in the [N II] 6548.10 band.
NW is up, SE down. Central star is visible in center for all velocities. This
sequence demonstrates the spherical nature of the shell in this region.
UVES long slit observations of Ghost Shell for multiple emission species.
Spectra have been aligned in velocity space for zero velocity reference
wavelengths for Ha, Hb and [S II] 6731. “GS” indicates ghost shell
feature, “FW” is homunculus front wall and “N” is background nebula.
3”
The sensitivity and resolution of UVES has allowed us to
generate a detailed map of the spatial distribution of the unusual
range of permitted and forbidden lines of the “heavy metals” that
are in the filaments. UVES has also allowed us to detect a
second, fainter filament above the one first observed by Zethson
et al.; this second, “Curved Filament” appears to be decelerating.
The SrFs provide challenges both in the mechanism for their
generation, and for the modes of excitation to provide the very
unusual relative line strengths. This remarkable region near the
central star appears to be related to the Weigelt C and D blobs
and, perhaps, a region of radio emission.
LF1
Equatorial Plane
4”
CF2?
(Left images) 1999 UVES long slit
observations of h Carina’s
0
Strontium Filaments along the
Homunculus axis of symmetry.
Shown for forbidden, neutral iron
(upper) and permitted, neutral iron
4” (lower). Data have been coadded
for indicated number of lines.
3”
CF1
LF3
2”
LF2
1”
LF1
0”
4”
CF2? CF1
CF1
3”
CF2?
The original feature observed by
3”
Zethson et al. is LF2, and forms
part of the Linear Filament (LF).
Also shown is the newly discovered
Curved Filament (CF), along with
2” four additional clumps. The clump
marked “LF1” corresponds to
Weigelt blobs C and D in position
and velocity.
1”
2”
LF2
LF2
(spurious
feature)
V II
(5 lines)
1”
LF1
LF1
0”
4”
3”
2”
LF2
Proposed geometry of Ghost Shell, shown with respect to the current
geometric model for the Homunculus. Ballistic (i.e., constant velocity)
expansion is assumed.
Ti II
(13 lines)
UVES long slit observations of h
Carina’s Strontium Filaments.
“AOS” indicates Homunculus axis of
symmetry.
0”
1”
LF1
-150
-100
-50
0”
0
Sc II
(6 lines)
(Left images) More data from the
1999 UVES long slit observations
of h Carina’s Strontium Filaments.
Data are coadded for the indicated
number of lines. Source species
are singly ionized titanium,
vanadium and scandium.
The feature correspond well in
velocity space to those in the iron
images. Note that LF1 (Weigelt
blobs C+D?) are present in all
permitted emission lines.