319 research outputs found
High resolution spectroscopy of SN~2023ixf's first week: Engulfing the Asymmetric Circumstellar Material
We present a series of high-resolution echelle spectra of SN~2023ixf in M101,
obtained nightly during the first week or so after discovery using PEPSI on the
LBT. NaID absorption in these spectra indicates a host reddening of
=0.031~mag and a systemic velocity of 7~km~s relative to the
average redshift of M101. Dramatic changes are seen in in the strength and
shape of strong emission lines emitted by CSM, including HeII4686,
CIV5801,5811, H, and NIV7109,7123. In general, these narrow lines
broaden to become intermediate-width lines before disappearing from the
spectrum within a few days, indicating a limited extent to the dense CSM of
around 20-30 AU (or \la10 cm). H persists in the spectrum
for about a week as an intermediate-width emission line with P~Cyg absorption
at 700-1300 km s arising in the post-shock shell of swept-up CSM. Early
narrow emission lines are blueshifted and indicate an expansion speed in the
pre-shock CSM of about 115 km s, but with even broader emission in
higher ionization lines. This is faster than the normal winds of red
supergiants, suggesting some mode of eruptive mass loss from the progenitor or
radiative acceleration of the CSM. A lack of narrow blueshifted absorption
suggests that most of the CSM is not along our line of sight. This and several
other clues indicate that the CSM of SN~2023ixf is significantly aspherical. We
find that CSM lines disappear after a few days because the asymmetric CSM is
engulfed by the SN photosphere.Comment: Accepted verion, 8/1
The R136 star cluster dissected with Hubble Space Telescope/STIS. I. Far-ultraviolet spectroscopic census and the origin of HeII 1640 in young star clusters
We introduce a HST/STIS stellar census of R136a, the central ionizing star
cluster of 30 Doradus. We present low resolution far-ultraviolet STIS/MAMA
spectroscopy of R136 using 17 contiguous 52x0.2 arcsec slits which together
provide complete coverage of the central 0.85 parsec (3.4 arcsec). We provide
spectral types of 90% of the 57 sources brighter than m_F555W = 16.0 mag within
a radius of 0.5 parsec of R136a1, plus 8 additional nearby sources including
R136b (O4\,If/WN8). We measure wind velocities for 52 early-type stars from CIV
1548-51, including 16 O2-3 stars. For the first time we spectroscopically
classify all Weigelt & Baier members of R136a, which comprise three WN5 stars
(a1-a3), two O supergiants (a5-a6) and three early O dwarfs (a4, a7, a8). A
complete Hertzsprung-Russell diagram for the most massive O stars in R136 is
provided, from which we obtain a cluster age of 1.5+0.3_-0.7 Myr. In addition,
we discuss the integrated ultraviolet spectrum of R136, and highlight the
central role played by the most luminous stars in producing the prominent HeII
1640 emission line. This emission is totally dominated by very massive stars
with initial masses above ~100 Msun. The presence of strong HeII 1640 emission
in the integrated light of very young star clusters (e.g A1 in NGC 3125)
favours an initial mass function extending well beyond a conventional upper
limit of 100 Msun. We include montages of ultraviolet spectroscopy for LMC O
stars in the Appendix. Future studies in this series will focus on optical
STIS/CCD medium resolution observations.Comment: 20 pages plus four Appendices providing LMC UV O spectral templates,
UV spectral atlas in R136, wind velocities of LMC O stars and photometry of
additional R136 source
Three-dimensional distribution of ejecta in Supernova 1987A at 10 000 days
Due to its proximity, SN 1987A offers a unique opportunity to directly
observe the geometry of a stellar explosion as it unfolds. Here we present
spectral and imaging observations of SN 1987A obtained ~10,000 days after the
explosion with HST/STIS and VLT/SINFONI at optical and near-infrared
wavelengths. These observations allow us to produce the most detailed 3D map of
H-alpha to date, the first 3D maps for [Ca II] \lambda \lambda 7292, 7324, [O
I] \lambda \lambda 6300, 6364 and Mg II \lambda \lambda 9218, 9244, as well as
new maps for [Si I]+[Fe II] 1.644 \mu m and He I 2.058 \mu m. A comparison with
previous observations shows that the [Si I]+[Fe II] flux and morphology have
not changed significantly during the past ten years, providing evidence that it
is powered by 44Ti. The time-evolution of H-alpha shows that it is
predominantly powered by X-rays from the ring, in agreement with previous
findings. All lines that have sufficient signal show a similar large-scale 3D
structure, with a north-south asymmetry that resembles a broken dipole. This
structure correlates with early observations of asymmetries, showing that there
is a global asymmetry that extends from the inner core to the outer envelope.
On smaller scales, the two brightest lines, H-alpha and [Si I]+[Fe II] 1.644
\mu m, show substructures at the level of ~ 200 - 1000 km/s and clear
differences in their 3D geometries. We discuss these results in the context of
explosion models and the properties of dust in the ejecta.Comment: Accepted for publication in Ap
Early Lightcurves of Type Ia Supernovae are Consistent with Nondegenerate Progenitor Companions
If Type Ia supernovae (SNe~Ia) result from a white dwarf being ignited by
Roche lobe overflow from a nondegenerate companion, then as the supernova
explosion runs into the companion star its ejecta will be shocked, causing an
early blue excess in the lightcurve. A handful of these excesses have been
found in single-object studies, but inferences about the population of SNe~Ia
as a whole have been limited because of the rarity of multiwavelength followup
within days of explosion. Here we present a three-year investigation yielding
an unbiased sample of nine nearby () SNe~Ia with exemplary early data.
The data are truly multiwavelength, covering and Swift bandpasses, and
also early, with an average first epoch 16.0 days before maximum light. Of the
nine objects, three show early blue excesses. We do not find enough statistical
evidence to reject the null hypothesis that SNe~Ia predominantly arise from
Roche-lobe-overflowing single-degenerate systems (). When looking at
the objects' colors, we find the objects are almost uniformly near-UV-blue, in
contrast to earlier literature samples which found that only a third of SNe~Ia
are near-UV-blue, and we find a seemingly continuous range of colors in
the days after explosion, again in contrast with earlier claims in the
literature. This study highlights the importance of early, truly
multiwavelength, high-cadence data in determining the progenitor systems of
SNe~Ia and in revealing their diverse early behavior.Comment: 28 pages, 10 figure
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