First Observations of Extended Objects with UVES/VLT: Carinae, the Discovery of the Ghost

Shell, and the Strontium FilamentsD. 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 Carinae. We discuss the UVES instrument and our observations of 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.

Carinae’s “Ghost Shell” Carinae’s Strontium Filaments

The Very Large Telescope/Ultraviolet andVisible Echelle Spectrograph

Carinae: Background

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 Carinae. We describe it's general properties and capabilities.

VLT Spectral Coverage

UVES Observational Capabilities

Parameter Blue Red

Wavelength range 300 - 500 nm 420 - 1100 nm

Resolution-slit product 41,400 arcsec 38,700 arcsec

Max. resolution ~80,000 ~110,000

Limiting magnitude(3hr, S/N~10, median seeing)

18.7 at R = 55,000 in U20.3 at R = 55,000 in V 18.7 at R = 90 000 in V

Overall detective quantum efficiency (DQE) (from top of the telescope, wide slit)

6 % at 320 nm15 % at 470 nm

18 % at 500 nm9 % at 900 nm (with EEV chip)

Cameradioptric 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 scale2K 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

Typical wavelength range/frame 80 nm in 30 orders 200 nm in 45 orders

Order separation (minimum) 12 arcsec or 50 pixels 12 arcsec or 75 pixels

UVES instrument layout (l.) and 3-D CAD depiction (r.)(with instrument cover removed)

Paranal observatory location in Chile’s Atacama desert offers some of the driest conditions in the southern hemisphere.

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 de-rotator, 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.

VLT Unit 4 during assembly CarinaNebula

Carinae and the Homunculus observed from Hubble Space Telescope.

One of the most massive stars in the galaxy, 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.

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 X-ray, UV, Visible, IR and RF portions of the frequency spectrum.

Carinae’s historical light curve.

1842 “Great Eruption”

1890 “Lesser Eruption”

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.

UVES long slit observations of Carinae used to discover and analyze the Ghost Shell feature. “AOS” indicates Homunculus axis of symmetry.

Line of sightd = ~2.2 kpc

Axis of Symmetry

Equatorial PlanePlane of the Sky

i = 40 deg~17 arcsec~37 kAU~200 light-days~0.2 pc

NWlobe

SElobe

5”GhostShell(continuous)

GhostShell(disrupted)

UVES long slit observations of Ghost Shell for multiple emission species. Spectra have been aligned in velocity space for zero velocity reference wavelengths for H, H and [S II] 6731. “GS” indicates ghost shell feature, “FW” is homunculus front wall and “N” is background nebula.

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).

Proposed geometry of Ghost Shell, shown with respect to the current geometric model for the Homunculus. Ballistic (i.e., constant velocity) expansion is assumed.

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.

-850 km/sec -800 km/sec -750 km/sec

-700 km/sec -650 km/sec -600 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 Carinae.

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.

UVES long slit observations of Carina’s Strontium Filaments. “AOS” indicates Homunculus axis of symmetry.

0”

1”

2”

3”

4”

-100 0-50-150

LinearFilament

CurvedFilament

CF1

CF2

LF2

0”

1”

2”

3”

4”

-100 0-50-150

(spuriousfeature)

LF3

LF2

LF1

CF2 CF1

[Fe I] (7 lines)

Fe I (16 lines)

0”

1”

2”

3”

4”

0”

1”

2”

3”

4”

0”

1”

2”

3”

4”

-100 0-50-150

CF1LF3

LF2

LF1

CF1

LF2LF1

LF2

LF1

CF2?

CF2?CF1

LF2

LF1

CF2?

-100 0-50-150

Ti II(13 lines)

V II(5 lines)

Sc II(6 lines)

(Left images) 1999 UVES long slit observations of Carina’s Strontium Filaments along the Homunculus axis of symmetry. Shown for forbidden, neutral iron (upper) and permitted, neutral iron (lower). Data have been coadded for indicated number of lines.

The original feature observed by Zethson et al. is LF2, and forms part of the Linear Filament (LF). Also shown is the newly discovered Curved Filament (CF), along with four additional clumps. The clump marked “LF1” corresponds to Weigelt blobs C and D in position and velocity.

(Left images) More data from the 1999 UVES long slit observations of 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.