7,518 research outputs found
Explosions of LBV and Post-LBV Stars
In this contributed talk I presented the observational evidence for supernova (SN) explosions of stars in the luminous blue variable (LBV) and the immediate post-LBV evolutionary phases. We now have compelling indications that two recent SNe of Type II-“narrow” (IIn) were the explosions
of LBVs, including the direct identification of the progenitor LBV for one of these
examples. A recent SN of Type Ic exploded as a helium star, two years after
the powerful LBV outburst of its progenitor. These cases were also discussed
by other presenters at this Workshop in some detail. I instead focus more on
another example, SN2001em, which was first identified as a Type Ib/c, but later
evolved to Type IIn. I argue that the progenitor of this SN exploded as a Wolf-
Rayet (WR) star, following an eruptive LBV phase. Furthermore, I suggest that
two “SN impostors,” i.e., extragalactic massive stars observed to undergo pre-SN
LBV eruptions (similar to η Carinae), may well have evolved to the WR phase
in real time
Luminous Blue Variable Stars In The Two Extremely Metal-Deficient Blue Compact Dwarf Galaxies DDO 68 and PHL 293B
We present photometric and spectroscopic observations of two luminous blue
variable (LBV) stars in two extremely metal-deficient blue compact dwarf (BCD)
galaxies, DDO 68 with 12+logO/H = 7.15 and PHL 293B with 12+logO/H = 7.72.
These two BCDs are the lowest-metallicity galaxies where LBV stars have been
detected, allowing to study the LBV phenomenon in the extremely low metallicity
regime, and shedding light of the evolution of the first generation of massive
stars born from primordial gas. We find that the strong outburst of the LBV
star in DDO 68 occurred sometime between February 2007 and January 2008. We
have compared the properties of the broad line emission in low-metallicity LBVs
with those in higher metallicity LBVs. We find that, for the LBV star in DDO
68, broad emission with a P Cygni profile is seen in both H and He I emission
lines. On the other hand, for the LBV star in PHL 293B, P Cygni profiles are
detected only in H lines. For both LBVs, no heavy element emission line such as
Fe II was detected. The Halpha luminosities of LBV stars in both galaxies are
comparable to the one obtained for the LBV star in NGC 2363 (Mrk 71) which has
a higher metallicity 12+logO/H = 7.89. On the other hand, the terminal
velocities of the stellar winds in both low-metallicity LBVs are high, ~800
km/s, a factor of ~4 higher than the terminal velocities of the winds in
high-metallicity LBVs. This suggests that stellar winds at low metallicity are
driven by a different mechanism than the one operating in high-metallicity
winds.Comment: 26 pages, 5 figures, accepted for publication in the Astrophysical
Journa
Infrared Observations of the Candidate LBV 1806-20 & Nearby Cluster Stars
We report near-infrared photometry, spectroscopy, and speckle imaging of the
hot, luminous star we identify as candidate LBV 1806-20. We also present
photometry and spectroscopy of 3 nearby stars, which are members of the same
star cluster containing LBV 1806-20 and SGR 1806-20. The spectroscopy and
photometry show that LBV 1806-20 is similar in many respects to the luminous
``Pistol Star'', albeit with some important differences. They also provide
estimates of the effective temperature and reddening of LBV 1806-20, and
confirm distance estimates, leading to a best estimate for the luminosity of
this star of . The nearby cluster stars have
spectral types and inferred absolute magnitudes which confirm the distance (and
thus luminosity) estimate for LBV 1806-20. If we drop kinematic measurements of
the distance ( kpc), we have a lower limit on the distance
of kpc, and on the luminosity of , based on
the cluster stars. If we drop both the kinematic and cluster star indicators
for distance, an ammonia absorption feature sets yet another lower limit to the
distance of kpc, with a corresponding luminosity estimate of for the candidate LBV 1806-20. Furthermore, based on very high
angular-resolution speckle images, we determine that LBV 1806-20 is not a
cluster of stars, but is rather a single star or binary system. Simple
arguments based on the Eddington luminosity lead to an estimate of the total
mass of LBV 1806-20 (single or binary) exceeding . We discuss
the possible uncertainties in these results, and their implications for the
star formation history of this cluster.Comment: 36 pages, including 8 figures (Figures 1 and 7 in JPG format due to
space); Accepted for publication in Ap
Crowded field 3D spectroscopy of LBV candidates in M33
We present integral field spectroscopy of the LBV candidate stars B416 and
v532 in the local group galaxy M33. B416 is surrounded by an elongated
ring-like nebula, which has a projected radius of 20x30 pc. From the datacube
we create ionization and radial velocity maps of the nebula. The excitation of
the gas decreases towards the outer part of the ring, while the inner part of
the nebula is filled with a more excited gas. In the EW direction the ring is
seen to expand with a maximum projected velocity amplitude of about 40 km/s.
The eastern part approaches the observer. We estimate the nebula dynamical
lifetime 8*10E5 years. It could be a residual MS bubble, which indicates a
main-sequence or pre-LBV status of the star. We classify B416 as an "iron star"
or B[e]-supergiant. In v532 an elongated nebula has been marginally detected.
The total projected size of the nebula along the main axis is 30 pc, and the
total radial velocity gradient is 44+/-11 km/s. v532 exhibits both strong
photometric and spectral variability. At the time of our observations it was in
an intermediate brightness state with a rich nitrogen spectrum. We classify
v532 as an LBV, showing LBV Ofpe/WN transitions. We stress the importance
of integral field spectroscopy as the optimal technique for studying nebulae
and the evolution of LBV-like stars in nearby galaxies.Comment: 12 pages, 10 Postscript figures, A&A accepte
The nature of V39: an LBV candidate or LBV impostor in the very low metallicity galaxy IC 1613?
[abridged]
Context: Very few examples of luminous blue variable (LBV) stars or LBV
candidates (LBVc) are known, particularly at metallicities below the SMC. The
LBV phase is crucial for the evolution of massive stars, and its behavior with
metallicity is poorly known. V39 in IC 1613 is a well-known photometric
variable, with B-band changes larger than 1mag. over its period. The star,
previously proposed to be a projection of a Galactic W Virginis and an IC 1613
red supergiant, shows features that render it a possible LBVc.
Method: We investigate mid-resolution blue and red VLT-VIMOS spectra of V39,
covering a time span of 40 days, and perform a quantitative analysis of the
combined spectrum using the model atmosphere code CMFGEN.
Results: We identify strong Balmer and FeII P-Cygni profiles, and a hybrid
spectrum resembling a B-A supergiant in the blue and a G-star in the red. No
significant Vrad variations are detected, and the spectral changes are small
over the photometric period. Our analysis places V39 in the low-luminosity part
of the LBV and LBVc region, but it is also consistent with a sgB[e] star.
Conclusions: The radial velocity indicates that V39 belongs to IC 1613. The
lack of Vrad changes and spectroscopic variations excludes binary scenarios.
The features observed are not consistent with a W Virginis star, and this
possibility is also discarded. We propose that the star is a B-A LBVc or sgB[e]
star surrounded by a thick disk precessing around it.
If confirmed, V39 would be the lowest metallicity resolved LBV candidate
known to date. Alternatively, it could represent a new transient phase of
massive star evolution, an LBV impostor.Comment: In press at A&A. 10 pages, 11 figure
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