58 research outputs found
Mid-Infrared diagnostics of metal-rich HII regions from VLT and Spitzer Spectroscopy of Young Massive Stars in W31
We present near-IR VLT/ISAAC and mid-IR Spitzer/IRS spectroscopy of the young
massive cluster in the W31 star-forming region. H-band spectroscopy provides
refined classifications for four cluster members O stars with respect to Blum
et al. In addition, photospheric features are detected in the massive Young
Stellar Object (mYSO) #26. Spectroscopy permits estimates of stellar
temperatures and masses, from which a cluster age of ~0.6 Myr and distance of
3.3 kpc are obtained, in excellent agreement with Blum et al. IRS spectroscopy
reveals mid-infrared fine structure line fluxes of [Ne II-III] and [S III-IV]
for four O stars and five mYSOs. In common with previous studies, stellar
temperatures of individual stars are severely underestimated from the observed
ratios of fine-structure lines, despite the use of contemporary stellar
atmosphere and photoionization models. We construct empirical temperature
calibrations based upon the W31 cluster stars of known spectral type,
supplemented by two inner Milky Way ultracompact (UC) HII regions whose
ionizing star properties are established. Calibrations involving [NeIII]
15.5um/[NeII] 12.8um, [SIV] 10.5um/[NeII] 12.8um or [ArIII] 9.0um/[NeII] 12.8um
have application in deducing the spectral types of early- to mid- O stars for
other inner Milky Way compact and UCHII regions. Finally, evolutionary phases
and timescales for the massive stellar content in W31 are discussed, due to the
presence of numerous young massive stars at different formation phases in a
`coeval' cluster.Comment: 16 pages, 13 figures, accepted for MNRA
The Type IIn Supernova SN 2010bt: The Explosion of a Star in Outburst
It is well known that massive stars (M > 8M(circle dot)) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN. 2010bt, which was classified as a Type. IIn. SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L-circle dot approximate to 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (similar to 5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN. 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor
SPIRITS 16tn in NGC 3556: A Heavily Obscured and Low-luminosity Supernova at 8.8 Mpc
We present the discovery by the SPitzer InfraRed Intensive Transients Survey (SPIRITS) of a likely supernova (SN) in NGC 3556 (M108) at only 8.8 Mpc that was not detected by optical searches. A luminous infrared (IR) transient at M [4.5] = −16.7 mag (Vega), SPIRITS 16tn is coincident with a dust lane in the inclined, star-forming disk of the host. Using observations in the IR, optical, and radio, we attempt to determine the nature of this event. We estimate A V ≈ 8–9 mag of extinction, placing it among the three most highly obscured IR-discovered SNe. The [4.5] light curve declined at a rate of 0.013 mag day−1, and the [3.6]–[4.5] color increased from 0.7 to gsim1.0 mag by 184.7 days post discovery. Optical/IR spectroscopy shows a red continuum but no clearly discernible features, preventing a definitive spectroscopic classification. Radio observations constrain the radio luminosity of SPIRITS 16tn to L ν lesssim 1024 erg s−1 Hz−1 between 3 and 15 GHz, excluding many varieties of core-collapse SNe. An SN Ia is ruled out by the observed IR color and lack of spectroscopic features from Fe-peak elements. SPIRITS 16tn was fainter at [4.5] than typical stripped-envelope SNe by ≈1 mag. Comparison of the spectral energy distribution to SNe II suggests that SPIRITS 16tn was both highly obscured and intrinsically dim, possibly akin to the low-luminosity SN 2005cs. We infer the presence of an IR dust echo powered by an initial peak luminosity of the transient of 5 × 1040 erg s−1 lesssim L peak lesssim 4 × 1043 erg s−1, consistent with the observed range for SNe II. This discovery illustrates the power of IR surveys to overcome the compounding effects of visible extinction and optically subluminous events in completing the inventory of nearby SNe
Light echoes reveal an unexpectedly cool Eta Carinae during its 19th-century Great Eruption
Eta Carinae (Eta Car) is one of the most massive binary stars in the Milky
Way. It became the second-brightest star in the sky during its mid-19th century
"Great Eruption," but then faded from view (with only naked-eye estimates of
brightness). Its eruption is unique among known astronomical transients in that
it exceeded the Eddington luminosity limit for 10 years. Because it is only 2.3
kpc away, spatially resolved studies of the nebula have constrained the ejected
mass and velocity, indicating that in its 19th century eruption, Eta Car
ejected more than 10 M_solar in an event that had 10% of the energy of a
typical core-collapse supernova without destroying the star. Here we report the
discovery of light echoes of Eta Carinae which appear to be from the 1838-1858
Great Eruption. Spectra of these light echoes show only absorption lines, which
are blueshifted by -210 km/s, in good agreement with predicted expansion
speeds. The light-echo spectra correlate best with those of G2-G5 supergiant
spectra, which have effective temperatures of ~5000 K. In contrast to the class
of extragalactic outbursts assumed to be analogs of Eta Car's Great Eruption,
the effective temperature of its outburst is significantly cooler than allowed
by standard opaque wind models. This indicates that other physical mechanisms
like an energetic blast wave may have triggered and influenced the eruption.Comment: Accepted for publication by Nature; 4 pages, 4 figures, SI: 6 pages,
3 figures, 5 table
Predicting the Presence of Companions for Stripped-envelope Supernovae: The Case of the Broad-lined Type Ic SN 2002ap
Many young, massive stars are found in close binaries. Using population synthesis simulations we predict the likelihood of a companion star being present when these massive stars end their lives as core-collapse supernovae (SNe). We focus on stripped-envelope SNe, whose progenitors have lost their outer hydrogen and possibly helium layers before explosion. We use these results to interpret new Hubble Space Telescope observations of the site of the broad-lined Type Ic SN 2002ap, 14 years post-explosion. For a subsolar metallicity consistent with SN 2002ap, we expect a main-sequence (MS) companion present in about two thirds of all stripped-envelope SNe and a compact companion (likely a stripped helium star or a white dwarf/neutron star/black hole) in about 5% of cases. About a quarter of progenitors are single at explosion (originating from initially single stars, mergers, or disrupted systems). All of the latter scenarios require a massive progenitor, inconsistent with earlier studies of SN 2002ap. Our new, deeper upper limits exclude the presence of an MS companion star >8–10 , ruling out about 40% of all stripped-envelope SN channels. The most likely scenario for SN 2002ap includes nonconservative binary interaction of a primary star initially . Although unlikely (<1% of the scenarios), we also discuss the possibility of an exotic reverse merger channel for broad-lined Type Ic events. Finally, we explore how our results depend on the metallicity and the model assumptions and discuss how additional searches for companions can constrain the physics that govern the evolution of SN progenitors.This work is based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. It is also based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory (JPL), California Institute of Technology, under a contract with NASA. Support was provided by NASA through grants GO-14075 and AR-14295 from STScI. We thank Andrew Dolphin for his patient advice on how best to implement artificial star tests in Dolphot. E.Z. is supported by a grant of the Netherlands Research School for Astronomy (NOVA). S.d.M. acknowledges support by a Marie Sklodowska-Curie Action (H2020 MSCA-IF-2014, project BinCosmos, ID 661502). A.V.F.'s group is also grateful for generous financial assistance from the Christopher R. Redlich Fund, the TABASGO Foundation, and NSF grant AST-1211916. N.S. is grateful for support from NSF grants AST-1312221 and AST-1515559. R.G.I. thanks the STFC for funding his Rutherford Fellowship under grant ST/L003910/1 and Churchill College, Cambridge, for his fellowship and access to their library
Long gamma-ray bursts and core-collapse supernovae have different environments
When massive stars exhaust their fuel they collapse and often produce the
extraordinarily bright explosions known as core-collapse supernovae. On
occasion, this stellar collapse also powers an even more brilliant relativistic
explosion known as a long-duration gamma-ray burst. One would then expect that
long gamma-ray bursts and core-collapse supernovae should be found in similar
galactic environments. Here we show that this expectation is wrong. We find
that the long gamma-ray bursts are far more concentrated on the very brightest
regions of their host galaxies than are the core-collapse supernovae.
Furthermore, the host galaxies of the long gamma-ray bursts are significantly
fainter and more irregular than the hosts of the core-collapse supernovae.
Together these results suggest that long-duration gamma-ray bursts are
associated with the most massive stars and may be restricted to galaxies of
limited chemical evolution. Our results directly imply that long gamma-ray
bursts are relatively rare in galaxies such as our own Milky Way.Comment: 27 pages, 4 figures, submitted to Nature on 22 August 2005, revised 9
February 2006, online publication 10 May 2006. Supplementary material
referred to in the text can be found at
http://www.stsci.edu/~fruchter/GRB/locations/supplement.pdf . This new
version contains minor changes to match the final published versio
A Blast Wave from the 1843 Eruption of Eta Carinae
Very massive stars shed much of their mass in violent precursor eruptions as
luminous blue variables (LBVs) before reaching their most likely end as
supernovae, but the cause of LBV eruptions is unknown. The 19th century
eruption of Eta Carinae, the prototype of these events, ejected about 12 solar
masses at speeds of 650 km/s, with a kinetic energy of almost 10^50 ergs. Some
faster material with speeds up to 1000-2000 km/s had previously been reported
but its full distribution was unknown. Here I report observations of much
faster material with speeds up to 3500-6000 km/s, reaching farther from the
star than the fastest material in earlier reports. This fast material roughly
doubles the kinetic energy of the 19th century event, and suggests that it
released a blast wave now propagating ahead of the massive ejecta. Thus, Eta
Car's outer shell now mimics a low-energy supernova remnant. The eruption has
usually been discussed in terms of an extreme wind driven by the star's
luminosity, but fast material reported here suggests that it was powered by a
deep-seated explosion rivalling a supernova, perhaps triggered by the
pulsational pair instability. This may alter interpretations of similar events
seen in other galaxies.Comment: 10 pages, 3 color figs, supplementary information. Accepted by Natur
The massive binary companion star to the progenitor of supernova 1993J
The massive star which underwent core-collapse to produce SN1993J was
identified as a non-variable red supergiant star in images of the galaxy M81
taken before explosion. However the stellar source showed an excess in UV and
B-band colours that suggested it had either a hot, massive companion star or
was embedded in an unresolved young stellar association. The spectra of SN1993J
underwent a remarkable transformation between a hydrogen-rich Type II supernova
and a helium-rich (hydrogen-deficient) Type Ib. The spectral and photometric
peculiarities were explained by models in which the 13-20 solar mass supergiant
had lost almost its entire hydrogen envelope to a close binary companion. The
binary scenario is currently the best fitting model for the production of such
type IIb supernovae, however the hypothetical massive companion stars have so
far eluded discovery. Here we report the results of new photometric and
spectroscopic observations of SN1993J, 10 years after explosion. At the
position of the fading SN we detect the unambiguous signature of a massive
star, the binary companion to the progenitor. This is evidence that this type
of SN originate in interacting binary systems.Comment: 18 pages (3 figures
SN 2009N: linking normal and subluminous Type II-P SNe
We present ultraviolet, optical, near-infrared photometry and spectroscopy of SN 2009N in NGC 4487. This object is a Type II-P supernova with spectra resembling those of subluminous II-P supernovae, while its bolometric luminosity is similar to that of the intermediate-luminosity SN 2008in. We created SYNOW models of the plateau phase spectra for line identification and to measure the expansion velocity. In the near-infrared spectra we find signs indicating possible weak interaction between the supernova ejecta and the pre-existing circumstellar material. These signs are also present in the previously unpublished near-infrared spectra of SN 2008in. The distance to SN 2009N is determined via the expanding photosphere method and the standard candle method as D = 21.6 +/- 1.1 Mpc. The produced nickel-mass is estimated to be similar to 0.020 +/- 0.004 M-circle dot. We infer the physical properties of the progenitor at the explosion through hydrodynamical modelling of the observables. We find the values ofthe total energy as similar to 0.48 x 10(51) erg, the ejected mass as similar to 11.5 M-circle dot, and the initial radius as similar to 287 R-circle dot.</p
Direct Evidence of Two-component Ejecta in Supernova 2016gkg from Nebular Spectroscopy*
Spectral observations of the type-IIb supernova (SN) 2016gkg at 300-800 days are reported. The spectra show nebular characteristics, revealing emission from the progenitor star's metal-rich core and providing clues to the kinematics and physical conditions of the explosion. The nebular spectra are dominated by emission lines of [O i] lambda lambda 6300, 6364 and [Ca ii] lambda lambda 7292, 7324. Other notable, albeit weaker, emission lines include Mg I] lambda 4571, [Fe ii] lambda 7155, O I lambda 7774, Ca II triplet, and a broad, boxy feature at the location of H alpha. Unlike in other stripped-envelope SNe, the [O i] doublet is clearly resolved due to the presence of strong narrow components. The doublet shows an unprecedented emission line profile consisting of at least three components for each [O i]lambda 6300, 6364 line: a broad component (width similar to 2000 km s(-1)), and a pair of narrow blue and red components (width similar to 300 km s(-1)) mirrored against the rest velocity. The narrow component appears also in other lines, and is conspicuous in [O i]. This indicates the presence of multiple distinct kinematic components of material at low and high velocities. The low-velocity components are likely to be produced by a dense, slow-moving emitting region near the center, while the broad components are emitted over a larger volume. These observations suggest an asymmetric explosion, supporting the idea of two-component ejecta that influence the resulting late-time spectra and light curves. SN 2016gkg thus presents striking evidence for significant asymmetry in a standard-energy SN explosion. The presence of material at low velocity, which is not predicted in 1D simulations, emphasizes the importance of multidimensional explosion modeling of SNe
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