62 research outputs found
N II 5668-5712, a New Class of Spectral Features in Eta Carinae
We report on the N II 5668-5712 emission and absorption lines in the spectrum
of Eta Carinae. Spectral lines of the stellar wind regions can be classified
into four physically distinct categories: 1) low-excitation emission such as H
I and Fe II, 2) higher excitation He I features, 3) the N II lines discussed in
this paper, and 4) He II emission. These categories have different combinations
of radial velocity behavior, excitation processes, and dependences on the
secondary star. The N II lines are the only known features that originate in
"normal" undisturbed zones of the primary wind but depend primarily on the
location of the hot secondary star. N II probably excludes some proposed
models, such as those where He I lines originate in the secondary star's wind
or in an accretion disk.Comment: 4 figures, 1 tabl
Why a Single-Star Model Cannot Explain the Bipolar Nebula of Eta Carinae
I examine the angular momentum evolution during the 1837-1856 Great Eruption
of the massive star Eta Carinae. I find that the new estimate of the mass blown
during that eruption implies that the envelope of Eta Car substantially
spun-down during the 20 years eruption. Single-star models, most of which
require the envelope to rotate close to the break-up velocity, cannot account
for the bipolar nebula (the Homunculus) formed from matter expelled in that
eruption. The kinetic energy and momentum of the Homunculus further constrains
single-star models. I discuss how Eta Car can fit into a unified model for the
formation of bipolar lobes where two oppositely ejected jets inflate two lobes
(or bubbles). These jets are blown by an accretion disk, which requires stellar
companions in the case of bipolar nebulae around stellar objects.Comment: ApJ, in press. New references and segments were adde
eta Carinae: linelist for the emission spectrum of the Weigelt blobs in the 1700 to 10 400 angstrom wavelength region
Aims. We present line identifications in the 1700 to 10 400 angstrom region for the Weigelt blobs B and D, located 0.'' 1 to 0 ''.3 NNW of Eta Carinae. The aim of this work is to characterize the behavior of these luminous, dense gas blobs in response to the broad highstate and the short low-state of. Carinae during its 5.54-year spectroscopic period. Methods. The spectra were recorded in a low state (March 1998) and an early high state (February 1999) with the Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) from 1640 to 10 400 angstrom using the 52 '' x 0.1 aperture centered on Eta Carinae at position angle, PA = 332 degrees. Extractions of the reduced spectrum including both Weigelt B and D, 0.'' 28 in length along the slit, were used to identify the narrow, nebular emission lines, measure their wavelengths and estimate their fluxes. Results. A linelist of 2500 lines is presented for the high and low states of the combined Weigelt blobs B and D. The spectra are dominated by emission lines from the iron-group elements, but include lines from lighter elements including parity-permitted and forbidden lines. A number of lines are fluorescent lines pumped by H Ly alpha. Other lines show anomalous excitation
Comparing Eta Carinae with the Red Rectangle
I compare the structures of the bipolar nebulae around the massive binary
system Eta Carinae and around the low mass binary system HD 44179. While Eta
Carinae is on its way to become a supernova, the Red Rectangle is on its way to
form a planetary nebula. Despite the two orders of magnitude difference in
mass, these two systems show several similarities, both in the properties of
the stellar binary systems and the nebulae. From this comparison and further
analysis of the accretion process during the 20 years Great Eruption of Eta
Carinae, I strengthen the binary model for the formation of its bipolar
nebula--the Homunculus. In the binary model a large fraction of the mass lost
by the primary star during the Great Eruption was transferred to the secondary
star (the companion); An accretion disk was formed around the companion, and
the companion launched two opposite jets. I show that the gravitational energy
of the mass accreted onto the secondary star during the Great Eruption can
account for the extra energy of the Great Eruption, both the radiated energy
and the kinetic energy in the Homunculus. I also conclude that neither the
proximity of the primary star in Eta Car to the Eddington luminosity, nor the
rotation of the primary star are related directly to the shaping of the
Homunculus. I speculate that the Great Eruption of Eta Carinae was triggered by
disturbance in the outer boundary of the convective region, most likely by
magnetic activity, that expelled the outer radiative zone.Comment: ApJ, in press (small changes from original version
Line Identifications in the Spectrum of eta Carinae as Observed in 1990-1991 with CCD Detectors
We have used the Cerro Tololo Inter-American Observatory telescopes andspectrographs to record emission lines in eta Carinae from 3093 to8956 Ă… with a gap between 4432 and 5696 Ă…. A resolving powerof about 20,000 was used throughout. Accurate wavelengths, peakintensities relative to the local continuum, and line identificationsare presented. The data are briefly discussed with respect to the stateof ionization present, the presence of oxygen lines, and the use of [SII] lines to derive a lower limit on the local electron density. We alsotabulate the wavelengths of interstellar absorption lines and diffuseinterstellar bands
Galactic Twins of the Ring Nebula Around SN1987A and a Possible LBV-like Phase for Sk-69 202
Some core-collapse supernovae show clear signs of interaction with dense
circumstellar material that often appears to be non-spherical. Circumstellar
nebulae around supernova progenitors provide clues to the origin of that
asymmetry in immediate pre-supernova evolution. Here I discuss outstanding
questions about the formation of the ring nebula around SN1987A and some
implications of similar ring nebulae around Galactic B supergiants. Several
clues hint that SN1987A's nebula may have been ejected in an LBV-like event,
rather than through interacting winds in a transition from a red supergiant to
a blue supergiant.Comment: 2 pages, to appear in procedings of "Massive stars: fundamental
parameters and circumstellar interactions", conference in honor of Virpi
Niemela's 70th birthda
Critical Differences and Clues in Eta Car's 2009 Event
We monitored Eta Carinae with HST WFPC2 and Gemini GMOS throughout the 2009
spectroscopic event, which was expected to differ from its predecessor in 2003
(Davidson et al. 2005). Here we report major observed differences between
events, and their implications. Some of these results were quite unexpected.
(1) The UV brightness minimum was much deeper in 2009. This suggests that
physical conditions in the early stages of an event depend on different
parameters than the "normal" inter-event wind. Extra mass ejection from the
primary star is one possible cause. (2) The expected He II 4687 brightness
maximum was followed several weeks later by another. We explain why this fact,
and the timing of the 4687 maxima, strongly support a "shock breakup"
hypothesis for X-ray and 4687 behavior as proposed 5-10 years ago. (3) We
observed a polar view of the star via light reflected by dust in the Homunculus
nebula. Surprisingly, at that location the variations of emission-line
brightness and Doppler velocities closely resembled a direct view of the star;
which should not have been true for any phenomena related to the orbit. This
result casts very serious doubt on all the proposed velocity interpretations
that depend on the secondary star's orbital motion. (4) Latitude-dependent
variations of H I, He I and Fe II features reveal aspects of wind behavior
during the event. In addition, we discuss implications of the observations for
several crucial unsolved problems.Comment: 45 pages, 9 figures, submitted to Ap
Identification of Emission Lines in the Low-Ionization Strontium Filament Near Eta Carinae
We have obtained deep spectra from 1640 to 10100A with the Space Telescope
Imaging Spectrograph (STIS) of the Strontium Filament, a largely neutral
emission nebulosity lying close to the very luminous star Eta Carinae and
showing an uncommon spectrum. Over 600 emission lines, both permitted and
forbidden, have been identified. The majority originates from neutral or
singly-ionized iron group elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni). Sr is the
only neutron capture element detected. The presence of Sr II, numerous strong
Ti II and V II lines and the dominance of Fe I over Fe II are notable
discoveries. While emission lines of hydrogen, helium, and nitrogen are
associable with other spatial structures at other velocities within the
Homunculus, no emission lines from these elements correspond to the spatial
structure or velocity of the Sr Filament. Moreover, no identified Sr Filament
emission line requires an ionization or excitation energy above approximately 8
eV. Ionized gas extends spatially along the aperture, oriented along the polar
axis of the Homunculus, and in velocity around the Strontium Filament. We
suggest that the Strontium Filament is shielded from ultraviolet radiation at
energies above 8 eV, but is intensely irradiated by the central star at
wavelengths longward of 1500A.Comment: 28 pages, 5 figures, 4 tables. Accepted by A&A. High resolution
pictures can be found at http://www.astro.lu.se/~henrikh/srpaper/srpaper.pd
The Structure of the Homunculus. III. Forming a Disk and Bipolar Lobes in a Rotating Surface Explosion
We present a semi-analytic model for shaping the nebula around eta Carinae
that accounts for the simultaneous production of bipolar lobes and an
equatorial disk through a rotating surface explosion. Material is launched
normal to the surface of an oblate rotating star with an initial kick velocity
that scales approximately with the local escape speed. Thereafter, ejecta
follow ballistic orbital trajectories, feeling only a central force
corresponding to a radiatively reduced gravity. Our model is conceptually
similar to the wind-compressed disk model of Bjorkman & Cassinelli, but we
modify it to an explosion instead of a steady line-driven wind, we include a
rotationally-distorted star, and we treat the dynamics somewhat differently.
Continuum-driving avoids the disk inhibition that normally operates in
line-driven winds. Our model provides a simple method by which rotating hot
stars can simultaneously produce intrinsically bipolar and equatorial mass
ejections, without an aspherical environment or magnetic fields. Although
motivated by eta Carinae, the model may have generic application to other LBVs,
B[e] stars, or SN1987A's nebula. When near-Eddington radiative driving is less
influential, our model generalizes to produce bipolar morphologies without
disks, as seen in many PNe.Comment: ApJ accepted, 9 page
The Binarity of Eta Carinae and its Similarity to Related Astrophysical Objects
I examine some aspects of the interaction between the massive star Eta
Carinae and its companion, in particular during the eclipse-like event, known
as the spectroscopic event or the shell event. The spectroscopic event is
thought to occur when near periastron passages the stellar companion induces
much higher mass loss rate from the primary star, and/or enters into a much
denser environment around the primary star. I find that enhanced mass loss rate
during periastron passages, if it occurs, might explain the high eccentricity
of the system. However, there is not yet a good model to explain the presumed
enhanced mass loss rate during periastron passages. In the region where the
winds from the two stars collide, a dense slow flow is formed, such that large
dust grains may be formed. Unlike the case during the 19th century Great
Eruption, the companion does not accrete mass during most of its orbital
motion. However, near periastron passages short accretion episodes may occur,
which may lead to pulsed ejection of two jets by the companion. The companion
may ionize a non-negligible region in its surrounding, resembling the situation
in symbiotic systems. I discuss the relation of some of these processes to
other astrophysical objects, by that incorporating Eta Car to a large class of
astrophysical bipolar nebulae.Comment: Updated version. ApJ, in pres
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