Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is ...subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks ("nickel heating"). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.
We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years ...away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts.
The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial ...mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses (Formula: see text). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 Formula: see text and contains 32 ± 12% more stars above 30 Formula: see text than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 Formula: see text, the IMF power-law exponent is Formula: see text, shallower than the Salpeter value of 2.35.
ABSTRACT
We report the discovery of J0624–6948, a low-surface brightness radio ring, lying between the Galactic Plane and the large magellanic cloud (LMC). It was first detected at 888 MHz with the ...Australian Square Kilometre Array Pathfinder (ASKAP), and with a diameter of ∼196 arcsec. This source has phenomenological similarities to odd radio circles (ORCs). Significant differences to the known ORCs – a flatter radio spectral index, the lack of a prominent central galaxy as a possible host, and larger apparent size – suggest that J0624–6948 may be a different type of object. We argue that the most plausible explanation for J0624–6948 is an intergalactic supernova remnant due to a star that resided in the LMC outskirts that had undergone a single-degenerate type Ia supernova, and we are seeing its remnant expand into a rarefied, intergalactic environment. We also examine if a massive star or a white dwarf binary ejected from either galaxy could be the supernova progenitor. Finally, we consider several other hypotheses for the nature of the object, including the jets of an active galactic nucleus (30Dor) or the remnant of a nearby stellar super-flare.
The survey for DUST in Nearby Galaxies with Spitzer (DUSTiNGS) identified several candidate Asymptotic Giant Branch (AGB) stars in nearby dwarf galaxies and showed that dust can form even in very ...metal-poor systems ( ). Here, we present a follow-up survey with WFC3/IR on the Hubble Space Telescope (HST), using filters that are capable of distinguishing carbon-rich (C-type) stars from oxygen-rich (M-type) stars: F127M, F139M, and F153M. We include six star-forming DUSTiNGS galaxies (NGC 147, IC 10, Pegasus dIrr, Sextans B, Sextans A, and Sag DIG), all more metal-poor than the Magellanic Clouds and spanning 1 dex in metallicity. We double the number of dusty AGB stars known in these galaxies and find that most are carbon rich. We also find 26 dusty M-type stars, mostly in IC 10. Given the large dust excess and tight spatial distribution of these M-type stars, they are most likely on the upper end of the AGB mass range (stars undergoing Hot Bottom Burning). Theoretical models do not predict significant dust production in metal-poor M-type stars, but we see evidence for dust excess around M-type stars even in the most metal-poor galaxies in our sample ( ). The low metallicities and inferred high stellar masses (up to ∼10 ) suggest that AGB stars can produce dust very early in the evolution of galaxies (∼30 Myr after they form), and may contribute significantly to the dust reservoirs seen in high-redshift galaxies.
We present K-band integral field spectroscopic observations towards 17 massive young stellar objects (YSOs) in the low-metallicity Small Magellanic Cloud (SMC) and two YSO candidates in the compact H ...II regions N81 and N88 A (also in the SMC). These sources, originally identified using Spitzer photometry and/or spectroscopy, have been resolved into 29 K-band continuum sources. By comparing Br gamma emission luminosities with those presented for a Galactic sample of massive YSOs, we find tentative evidence for increased accretion rates in the SMC. Around half of our targets exhibit emission-line (Br gamma , He I and H sub( 2)) morphologies that extend significantly beyond the continuum source and we have mapped both the emission morphologies and the radial velocity fields. This analysis also reveals evidence for the existence of ionized low-density regions in the centre outflows from massive YSOs. Additionally, we present an analysis of optical spectra towards a similar sample of massive YSOs in the SMC, revealing that the optical emission is photoexcited and originates near the outer edges of molecular clouds, and is therefore consistent with a high mean-free path of UV photons in the interstellar medium (ISM) of the SMC. Finally, we discuss the sample of YSOs in an evolutionary context incorporating the results of previous infrared and radio observations, as well as the near-infrared and optical observations presented in this work. Our spectroscopic analysis in both the K band and the optical regimes, combined with previously obtained infrared and radio data, exposes differences between properties of massive YSOs in our own Galaxy and the SMC, including tracers of accretion, discs and YSO-ISM interactions.
We present an empirical determination of the mass-loss rate as a function of stellar luminosity and effective temperature, for oxygen-rich dust-enshrouded Asymptotic Giant Branch stars and red ...supergiants. To this aim we obtained optical spectra of a sample of dust-enshrouded red giants in the Large Magellanic Cloud, which we complemented with spectroscopic and infrared photometric data from the literature. Two of these turned out to be hot emission-line stars, of which one is a definite Be star. The mass-loss rates were measured through modelling of the spectral energy distributions. We thus obtain the mass-loss rate formula $\log \dot{M} = -5.65 + 1.05 \log ( L / 10\,000\, {L}_\odot ) -6.3 \log ( T_{\rm eff} / 3500\, {\rm K} )$, valid for dust-enshrouded red supergiants and oxygen-rich AGB stars. Despite the low metallicity of the LMC, both AGB stars and red supergiants are found at late spectral types. A comparison with galactic AGB stars and red supergiants shows excellent agreement between the mass-loss rate as predicted by our formula and that derived from the 60 μm flux density for dust-enshrouded objects, but not for optically bright objects. We discuss the possible implications of this for the mass-loss mechanism.
The VLT-FLAMES Tarantula Survey Schneider, F. R. N.; Ramírez-Agudelo, O. H.; Tramper, F. ...
Astronomy and astrophysics (Berlin),
10/2018, Volume:
618
Journal Article
Peer reviewed
Open access
The 30 Doradus (30 Dor) nebula in the Large Magellanic Cloud (LMC) is the brightest HII region in the Local Group and a prototype starburst similar to those found in high redshift galaxies. It is ...thus a stepping stone to understand the complex formation processes of stars in starburst regions across the Universe. Here, we have studied the formation history of massive stars in 30 Dor using masses and ages derived for 452 mainly OB stars from the spectroscopic VLT-FLAMES Tarantula Survey (VFTS). We find that stars of all ages and masses are scattered throughout 30 Dor. This is remarkable because it implies that massive stars either moved large distances or formed independently over the whole field of view in relative isolation. We find that both channels contribute to the 30 Dor massive star population. Massive star formation rapidly accelerated about 8 Myr ago, first forming stars in the field before giving birth to the stellar populations in NGC 2060 and NGC 2070. The R136 star cluster in NGC 2070 formed last and, since then, about 1 Myr ago, star formation seems to be diminished with some continuing in the surroundings of R136. Massive stars within a projected distance of 8 pc of R136 are not coeval but show an age range of up to 6 Myr. Our mass distributions are well populated up to 200 M⊙. The inferred IMF is shallower than a Salpeter-like IMF and appears to be the same across 30 Dor. By comparing our sample of stars to stellar models in the Hertzsprung–Russell diagram, we find evidence for missing physics in the models above log L/L⊙ = 6 that is likely connected to enhanced wind mass loss for stars approaching the Eddington limit. Our work highlights the key information about the formation, evolution and final fates of massive stars encapsulated in the stellar content of 30 Dor, and sets a new benchmark for theories of massive star formation in giant molecular clouds.
We estimate the total dust input from the cool evolved stars in the Small Magellanic Cloud, using the 8 mu m excess emission as a proxy for the dust-production rate (DPR). We find that asymptotic ...giant branch (AGB) and red supergiant (RSG) stars produce (8.6-9.5) x 10 super(-7) M sub(middot in circle) yr super(-1) of dust, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%-50% uncertainty in individual DPRs). RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the so-called extreme AGB stars) account for 87%-89% of the total dust input from cool evolved stars. We also estimate the dust input from hot stars and supernovae (SNe), and find that if SNe produce 10 super(-3) M sub(middot in circle) of dust each, then the total SN dust input and AGB input are roughly equivalent. We consider several scenarios of SN dust production and destruction and find that the interstellar medium (ISM) dust can be accounted for solely by stellar sources if all SNe produce dust in the quantities seen around the dustiest examples and if most SNe explode in dense regions where much of the ISM dust is shielded from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust. Without a net positive contribution from SNe to the dust budget, this suggests that dust must grow in the ISM or be formed by another unknown mechanism.
ABSTRACT
We present results from an analysis of ∼29 000 RR Lyrae stars located in the Large Magellanic Cloud (LMC). For these objects, near-infrared time-series photometry from the VISTA survey of ...the Magellanic Clouds system (VMC) and optical data from the Optical Gravitational Lensing Experiment (OGLE) IV survey and the Gaia Data Release 2 catalogue of confirmed RR Lyrae stars were exploited. Using VMC and OGLE IV magnitudes we derived period–luminosity (PL), period–luminosity–metallicity (PLZ), period–Wesenheit (PW), and period–Wesenheit–metallicity (PWZ) relations in all available bands. More that 7000 RR Lyrae were discarded from the analysis because they appear to be overluminous with respect to the PL relations. The $PL_{K_{\mathrm{s}}}$ relation was used to derive individual distance to ${\sim}22\, 000$ RR Lyrae stars, and study the three-dimensional structure of the LMC. The distribution of the LMC RR Lyrae stars is ellipsoidal with the three axis S1 = 6.5 kpc, S2 = 4.6 kpc, and S3 = 3.7 kpc, inclination i = 22 ± 4° relative to the plane of the sky and position angle of the line of nodes θ = 167 ± 7° (measured from north to east). The north-eastern part of the ellipsoid is closer to us and no particular associated substructures are detected and neither any metallicity gradient.
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