21 research outputs found
Massive young stellar objects in the N66/NGC346 region of the SMC
We present HK spectra of three sources located in the N66 region of the Small
Magellanic Cloud. The sources display prominent stellar Br Gamma and extended
H2 emission, and exhibit infrared excesses at lambda > 2 micron. Based on their
spectral features, and photometric spectral energy distributions, we suggest
that these sources are massive young stellar objects (mYSOs). The findings are
interpreted as evidence of on-going high mass star formation in N66.Comment: Accepted for publication on Astronomy and Astrophysics Journal,
acceptance date 21/03/2018 (includes 12 pages, 5 figures
Pillars of creation amongst destruction: Star formation in molecular clouds near R136 in 30 Doradus
New sensitive CO(2-1) observations of the 30 Doradus region in the Large
Magellanic Cloud are presented. We identify a chain of three newly discovered
molecular clouds we name KN1, KN2 and KN3 lying within 2--14 pc in projection
from the young massive cluster R136 in 30 Doradus. Excited H 2.12m
emission is spatially coincident with the molecular clouds, but ionized
Br emission is not. We interpret these observations as the tails of
pillar-like structures whose ionized heads are pointing towards R136. Based on
infrared photometry, we identify a new generation of stars forming within this
structure.Comment: Accepted for publication in ApJ (includes 13 pages, 8 figures). For
higher resolution figures please see
http://www.das.uchile.cl/~vkalari/staplervk.pd
Understanding the chemical evolution of blue Edge-on Low Surface Brightness Galaxies
We present a sample of 330 blue edge-on low surface brightness galaxies
(ELSBGs). To understand the chemical evolution of LSBGs, we derived the
gas-phase abundance and the [/Fe] ratio. Compared with star-forming
galaxies, ELSBGs show a flatter trend in the mass-metallicity ()
relation, suggesting that the oxygen abundance enhancement is inefficient. We
focus on 77 ELSBGs with HI data and found the closed-box model can not explain
their gas fraction and metallicity relation, implying that infall and/or
outflow is needed. We derived the [/Fe] ratio of normal ELSBG (
10M) and massive ELSBG ( 10M) using single
stellar population grids from MILES stellar library. The mean [/Fe]
ratios are 0.18 and 0.4 for normal ELSBG and massive ELSBG, respectively. We
discussed that the long time-scale of star-formation, and/or metal-rich gas
outflow event caused by SNe Ia winds are likely responsible for the
-enhancement of massive ELSBGs.Comment: 9 pages, 9 figures, Accepted for publication in Ap
GHOST Commissioning Science Results II: a very metal-poor star witnessing the early Galactic assembly
This study focuses on Pristine (hereafter P180956,
[Fe/H] ), a star selected from the Pristine Inner Galaxy Survey
(PIGS), and followed-up with the recently commissioned Gemini High-resolution
Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST
spectrograph's high efficiency in the blue spectral region (~\AA)
enables the detection of elemental tracers of early supernovae (e.g. Al, Mn,
Sr, Eu), which were not accessible in the previous analysis of P180956. The
star exhibits chemical signatures resembling those found in ultra-faint dwarf
systems, characterised by very low abundances of neutron-capture elements (Sr,
Ba, Eu), which are uncommon among stars of comparable metallicity in the Milky
Way. Our analysis suggests that P180956 bears the chemical imprints of a small
number (2 or 4) of low-mass hypernovae (\sim10-15\msun), which are needed to
reproduce the abundance pattern of the light-elements (e.g. [Si, Ti/Mg, Ca]
), and one fast-rotating intermediate-mass supernova (\sim300\kms,
\sim80-120\msun). Both types of supernovae explain the high [Sr/Ba] of
P180956 (). The small pericentric (\sim0.7\kpc) and apocentric
(\sim13\kpc) distances and its orbit confined to the plane (\lesssim
2\kpc), indicate that this star was likely accreted during the early Galactic
assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a
system similar to an ultra-faint dwarf galaxy accreted either alone, as one of
the low-mass building blocks of the proto-Galaxy, or as a satellite of
Gaia-Sausage-Enceladus. The combination of Gemini's large aperture with GHOST's
high efficiency and broad spectral coverage makes this new spectrograph one of
the leading instruments for near-field cosmology investigations.Comment: Submitted to MNRAS. 8 figures, 15page
SPLUS J142445.34-254247.1: An R-Process Enhanced, Actinide-Boost, Extremely Metal-Poor star observed with GHOST
We report on the chemo-dynamical analysis of SPLUS J142445.34-254247.1, an
extremely metal-poor halo star enhanced in elements formed by the rapid
neutron-capture process. This star was first selected as a metal-poor candidate
from its narrow-band S-PLUS photometry and followed up spectroscopically in
medium-resolution with Gemini South/GMOS, which confirmed its low-metallicity
status. High-resolution spectroscopy was gathered with GHOST at Gemini South,
allowing for the determination of chemical abundances for 36 elements, from
carbon to thorium. At [Fe/H]=-3.39, SPLUS J1424-2542 is one of the lowest
metallicity stars with measured Th and has the highest logeps(Th/Eu) observed
to date, making it part of the "actinide-boost" category of r-process enhanced
stars. The analysis presented here suggests that the gas cloud from which SPLUS
J1424-2542 was formed must have been enriched by at least two progenitor
populations. The light-element (Z<=30) abundance pattern is consistent with the
yields from a supernova explosion of metal-free stars with 11.3-13.4 Msun, and
the heavy-element (Z>=38) abundance pattern can be reproduced by the yields
from a neutron star merger (1.66Msun and 1.27Msun) event. A kinematical
analysis also reveals that SPLUS J1424-2542 is a low-mass, old halo star with a
likely in-situ origin, not associated with any known early merger events in the
Milky Way.Comment: 26 pages, 11 figures, accepted for publication on Ap
The Magellanic Bridge Cluster NGC 796: Deep Optical AO Imaging Reveals the Stellar Content and Initial Mass Function of a Massive Open Cluster
Probing the early Milky Way with GHOST spectra of an extremely metal-poor star in the Galactic disc
Pristine_183.6849 + 04.8619 (P1836849) is an extremely metal-poor ([Fe/H] = -3.3 ± 0.1) star on a prograde orbit confined to the Galactic disc. Such stars are rare and may have their origins in protogalactic fragments that formed the early Milky Way, in low-mass satellites accreted later, or forming in situ in the Galactic plane. Here, we present a chemo-dynamical analysis of the spectral features between 3700-11 000 Å from a high-resolution spectrum taken during Science Verification of the new Gemini High-resolution Optical SpecTrograph. Spectral features for many chemical elements are analysed (Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni), and valuable upper limits are determined for others (C, Na, Sr, Ba). This main sequence star exhibits several rare chemical signatures, including (i) extremely low metallicity for a star in the Galactic disc, (ii) very low abundances of the light α-elements (Na, Mg, Si) compared to other metal-poor stars, and (iii) unusually large abundances of Cr and Mn, where [Cr, Mn/Fe]NLTE > +0.5. A comparison to theoretical yields from supernova models suggests that two low-mass Population III objects (one 10 M· supernova and one 17 M· hypernova) can reproduce the abundance pattern well (reduced χ2 < 1). When this star is compared to other extremely metal-poor stars on quasi-circular, prograde planar orbits, differences in both chemistry and kinematics imply there is little evidence for a common origin. The unique chemistry of P1836849 is discussed in terms of the earliest stages in the formation of the Milky Way.</p
The 30 Doradus Molecular Cloud at 0.4 pc Resolution with the Atacama Large Millimeter/submillimeter Array: Physical Properties and the Boundedness of CO-emitting Structures
International audienceWe present results of a wide-field (approximately 60 × 90 pc) Atacama Large Millimeter/submillimeter Array mosaic of CO(2-1) and 13CO(2-1) emission from the molecular cloud associated with the 30 Doradus star-forming region in the Large Magellanic Cloud (LMC). Three main emission complexes, including two forming a bow-tie-shaped structure extending northeast and southwest from the central R136 cluster, are resolved into complex filamentary networks. Consistent with previous studies, we find that the central region of the cloud has higher line widths at a fixed size relative to the rest of the molecular cloud and to other LMC clouds, indicating an enhanced level of turbulent motions. However, there is no clear trend in gravitational boundedness (as measured by the virial parameter) with distance from R136. Structures observed in 13CO are spatially coincident with filaments and are close to a state of virial equilibrium. In contrast, 12CO structures vary greatly in virialization, with low CO surface brightness structures outside of the main filamentary network being predominantly unbound. The low surface brightness structures constitute ~10% of the measured CO luminosity; they may be shredded remnants of previously star-forming gas clumps, or alternatively the CO-emitting parts of more massive, CO-dark structures
The Accretion Dicsc in Halfa with OmegaCAM (ADHOC) Survey
We present the first results of the Accretion Discs in Hα with OmegaCAM (ADHOC) survey, which aims to perform a deep and homogeneous photometric study of pre-main sequence (PMS) stars in a number of nearby star-forming regions. We took advantage of the exquisite image quality and wide-field capabilities of OmegaCAM at the VLT Survey Telescope (VST) to perform multi-band (ugri and Hα), deep (iSDSS < 22 mag), homogeneous and wide-field (covering tens of parsecs) observations of eight star-forming regions: the Orion Nebula Cluster, Lupus, Sco-Cen, Haffner 18, Vela OB2, Eta Cha, Chamaeleon and Ophiuchus. Using a robust method to identify PMS stars through their photometric excess in the Hα band, we aim to measure physical parameters (including mass accretion rates) for over 10 000 PMS stars. Direct comparison with low-resolution spectroscopy confirms that the objects with Hα excess emission that are detected photometrically are bona-fide PMS stars. The first results from this study clearly demonstrate the validity of the observational approach to unveiling complex stellar populations in young clusters.Fil: Beccari, Giacomo. European Southern Observatory Chile; ChileFil: Petr-Gotzens, Monika G.. European Southern Observatory Chile; ChileFil: Boffin, Henri M. J.. European Southern Observatory Chile; ChileFil: Jerabkova, Tereza. European Southern Observatory Chile; ChileFil: Romaniello, Martino. European Southern Observatory Chile; ChileFil: Areal, MarÃa Belén. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Carraro, Giovanni. Dipartimento Di Fisica E Astronomia Galileo Galile; ItaliaFil: Celis Peña, Mariela Fernanda. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: De Marchi, Guido De. European Space Research And Technology Centre; PaÃses BajosFil: de Wit, Willem-Jan. European Southern Observatory Chile; ChileFil: Drew, Janet E.. Centre For Astrophysics Research; Reino UnidoFil: Fedele, Davide. Osservatorio Astrofisico Di Arcetri; ItaliaFil: Ferrero, Leticia Virginia. Consejo Nacional de Investigaciones CientÃficas y Técnicas; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; ArgentinaFil: Kalari, Venu M.. Universidad de Santiago de Chile; ChileFil: Manara, Carlo F.. European Southern Observatory Chile; ChileFil: Mardones, Diego. Universidad de Santiago de Chile; ChileFil: Martin, Eduardo L.. Centro de Astrobiologia Madrid; EspañaFil: Meza, Erick. Université Pierre et Marie Curie; FranciaFil: Mieske, Steffen. Universidad de Santiago de Chile; ChileFil: Panagia, Nino. Space Telescope Science Institute; Estados UnidosFil: Testi, Leonardo. European Southern Observatory Chile; ChileFil: Vink, Jorick S.. Armagh Observatory; Reino UnidoFil: Walsh, Jeremy R.. European Southern Observatory Chile; ChileFil: Wright, Nick J.. Keele University.; Reino Unid
GHOST commissioning science results - II: a very metal-poor star witnessing the early galactic assembly
International audienceThis study focuses on Pristine-294759.8 (hereafter P180956, [Fe/H] = -1.95 ± 0.02), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph's high efficiency in the blue spectral region (3700-4800 Å) enables the detection of elemental tracers of early supernovae (e.g. Al, Mn, Sr, and Eu). The star exhibits chemical signatures resembling those found in ultrafaint dwarf (UFD) systems, characterized by very low abundances of neutron-capture elements (Sr, Ba, and Eu), which are uncommon among stars in the Milky Way halo. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae (), which are needed to mostly reproduce the abundance pattern of the light-elements (e.g. [Si, Ti/Mg, Ca] ~0.6), and one fast-rotating intermediate-mass supernova (, ), which is the main channel contributing to the high [Sr/Ba] (~+1.2). The small pericentric () and apocentric () distances and its orbit confined to the plane () indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to a UFD galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia-Sausage-Enceladus. The combination of Gemini's large aperture with GHOST's high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations