21 research outputs found
Binary energy source of the HH 250 outflow and its circumstellar environment
Herbig-Haro flows are signposts of recent major accretion and outflow
episodes. We aim to determine the nature and properties of the little-known
outflow source HH 250-IRS, which is embedded in the Aquila clouds. We have
obtained adaptive optics-assisted L-band images with the NACO instrument on the
Very Large Telescope (VLT), together with N- and Q-band imaging with VISIR also
on the VLT. Using the SINFONI instrument on the VLT we carried out H- and
K-band integral field spectroscopy of HH 250-IRS, complemented with spectra
obtained with the SpeX instrument at the InfraRed Telescope Facility (IRTF) in
the JHKL bands. Finally, the SubMillimeter Array (SMA) interferometer was used
to study the circumstellar environment of HH 250-IRS at 225 and 351 GHz with CO
(2-1) and CO (3-2) maps and 0.9 mm and 1.3 mm continuum images. The HH 250-IRS
source is resolved into a binary with 0''53 separation, corresponding to 120 AU
at the adopted distance of 225 pc. The individual components show heavily
veiled spectra with weak CO absorption indicative of late-type stars. Both are
Class I sources, but their spectral energy distributions between 1.5 m and
19 m differ markedly and suggest the existence of a large cavity around
one of the components. The millimeter interferometric observations indicate
that the gas mainly traces a circumbinary envelope or disk, while the dust
emission is dominated by one of the circumstellar envelopes. HH 250-IRS is a
new addition to the handful of multiple systems where the individual stellar
components, the circumstellar disks and a circumbinary disk can be studied in
detail, and a rare case among those systems in which a Herbig-Haro flow is
present.Comment: Accepted for publication by Astronomy and Astrophysic
Multiplicity, kinematics and rotation rates of very young brown dwarfs in ChaI
We have studied twelve very young (1-5Myr) bona fide and candidate brown
dwarfs in the ChaI star forming region in terms of their kinematic properties,
the occurrence of multiple systems among them as well as their rotational
characteristics. Based on high-resolution spectra taken with UVES at the VLT
(8.2m), radial and rotational velocities have been measured. A kinematic study
of the sample showed that their radial velocity dispersion is relatively small
suggesting that they are not ejected during their formation as proposed in
recent formation scenarios. By means of time-resolved UVES spectra, a radial
velocity survey for close companions to the targets was conducted. The radial
velocities of the targets turned out to be rather constant setting upper limits
for the mass Msini of possible companions to 0.1 - 2 M_Jup. These findings hint
at a rather low (<10%) multiplicity fraction of the studied brown dwarfs.
Furthermore, a photometric monitoring campaign of the targets yielded the
determination of rotational periods for three brown dwarf candidates in the
range of 2.2 to 3.4 days. These are the first rotational periods for very young
brown dwarfs and among the first for brown dwarfs at all.Comment: Proceeding of IAU Colloquium No. 211 on Brown Dwarfs, Hawai'i, May
2002 (7 pages, 5 figures
Spectroscopic characterization of the known O-star population in Cygnus OB2. Evidence of multiple star-forming bursts
Context. Cygnus OB2 provides a unique insight into the high-mass stellar content in one of the largest groups of young massive stars in our Galaxy. Although several studies of its massive population have been carried out over the last decades, an extensive spectroscopic study of the whole known O-star population in the association is still lacking. Aims. We aim to carry out a spectroscopic characterization of all the currently known O stars in Cygnus OB2, determining the distribution of rotational velocities and accurate stellar parameters to obtain an improved view of the evolutionary status of the region. Methods. Based on existing and new optical spectroscopy, we performed a detailed quantitative spectroscopic analysis of all the known O-type stars identified in the association. For this purpose, we used the user-friendly iacob-broad and iacob-gbat automatized tools, FASTWIND stellar models, and astrometry provided by the Gaia second data release. Results. We created the most complete spectroscopic census of O stars carried out so far in Cygnus OB2 using already existing and new spectroscopy. We present the spectra for 78 O-type stars, from which we identify new binary systems, obtain the distribution of rotational velocities, and determine the main stellar parameters for all the stars in the region that have not been detected as double-line spectroscopic binaries. We also derive radii, luminosities, and masses for those stars with reliable Gaia astrometry, in addition to creating the Hertzsprung-Russell Diagram to interpret the evolutionary status of the association. Finally, we inspect the dynamical state of the population and identify runaway candidates. Conclusions. Our spectroscopic analysis of the O-star population in Cygnus OB2 has led to the discovery of two new binary systems and the determination of the main stellar parameters, including rotational velocities, luminosities, masses, and radii for all identified stars. This work has shown the improvement reached when using accurate spectroscopic parameters and astrometry for the interpretation of the evolutionary status of a population, revealing, in the case of Cygnus OB2, at least two star-forming bursts at ~3 and ~5 Myr. We find an apparent deficit of very fast rotators in the distribution of rotational velocities. The inspection of the dynamical distribution of the sample has allowed us to identify nine O stars with peculiar proper motions and discuss a possible dynamical ejection scenario or past supernova explosions in the region.We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under the grants AYA2012-39364-C02-01, AYA 2015-68012-C2-01, Severo Ochoa SEV-2015-0548 and PGC2018-093741-B-C21/C22 (MICIU/AEI/FEDER, UE)
The massive relic galaxy NGC 1277 is dark matter deficient. From dynamical models of integral-field stellar kinematics out to five effective radii
According to the CDM cosmology, present-day galaxies with stellar
masses should contain a sizable fraction of
dark matter within their stellar body. Models indicate that in massive
early-type galaxies (ETGs) dark matter should account for of the
dynamical mass within five effective radii (). Most massive ETGs
have been shaped through a two-phase process: the rapid growth of a compact
core was followed by the accretion of an extended envelope through mergers. The
exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG
population at . The best relic galaxy candidate discovered to date
is NGC 1277, in the Perseus cluster. We used deep integral field GCMS data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to ). By using Jeans anisotropic modelling we find a negligible dark
matter fraction within (; two-sigma
confidence level), which is in tension with the expectation. Since the lack of
an extended envelope would reduce dynamical friction and prevent the accretion
of an envelope, we propose that NGC 1277 lost its dark matter very early or
that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals suggesting that some relic galaxies may result
from dark matter stripping as they fell in and interacted within galaxy
clusters. Alternatively, NGC 1277 might have been born in a high-velocity
collision of gas-rich proto-galactic fragments, where dark matter left behind a
disc of dissipative baryons. We speculate that the relative velocities of
required for the latter process to happen were
possible in the progenitors of the present-day rich galaxy clusters.Comment: Accepted for publication in A&
X-ray and IR Point Source Identification and Characteristics in the Embedded, Massive Star-Forming Region RCW 108
We report on the results of an approximately 90 ks Chandra observation of a
complex region that hosts multiple sites of recent and active star formation in
ARA OB1a. The field is centered on the embedded cluster RCW 108-IR and includes
and a large portion of the open cluster NGC 6193. We detect over 420 X-ray
sources in the field and combined these data with deep near-IR, Spitzer/IRAC
and MSX mid-IR data. We find about 360 of the X-ray sources have near--IR
counterparts. We divide the region into 5 parts based on the X-ray point source
characteristics and extended 8 micron emission. The most clearly defined
regions are the central region - identified by embedded sources with high
luminosities in the both the near-IR and X-ray as well as high X-ray
temperatures (about 3 keV) and the eastern region - identified by low
extinction and 1 keV X-ray temperatures. Other regions, identified by their
directional relationship to RCW 108-IR are less uniform - representing
combinations of the first two regions, independent star formation epochs, or
both. Over 18% percent of the cluster members with over 100 counts exhibit
flares. Overall about 50% of the stars appear to have optically thick disks
when IRAC data are employed. The largest fraction of X-ray sources are best
described as possessing some disk material via a more detailed extinction
fitting. We estimate that the total number of pre--main sequence stars in the
field is about 1600. Approximately 800 are confined to (1.1 pc) central region.Comment: 63 pages including 18 figures, and 15 tables. Tables 1,2,5,7,10,and
11 have been stubbed in the text and included as ancillary files. Accepted by
the Astronomical Journa
The nature of the Cygnus extreme B supergiant 2MASS J20395358+4222505
2MASS J20395358+4222505 is an obscured early B supergiant near the massive OB star association Cygnus OB2. Despite its bright infrared magnitude (Ks = 5.82) it has remained largely ignored because of its dim optical magnitude (B = 16.63, V = 13.68). In a previous paper, we classified it as a highly reddened, potentially extremely luminous, early B-type supergiant. We obtained its spectrum in the U, B and R spectral bands during commissioning observations with the instrument MEGARA at the Gran Telescopio CANARIAS. It displays a particularly strong Hα emission for its spectral type, B1 Ia. The star seems to be in an intermediate phase between supergiant and hypergiant, a group that it will probably join in the near (astronomical) future. We observe a radial velocity difference between individual observations and determine the stellar parameters, obtaining Teff = 24 000 K and log gc = 2.88 ± 0.15. The rotational velocity found is large for a B supergiant, v sin i = 110 ± 25 kms−1. The abundance pattern is consistent with solar, with a mild C underabundance (based on a single line). Assuming that J20395358+4222505 is at the distance of Cyg OB2, we derive the radius from infrared photometry, finding R = 41.2 ± 4.0 R⊙, log(L/L⊙) = 5.71 ± 0.04 and a spectroscopic mass of 46.5 ± 15.0 M⊙. The clumped mass-loss rate (clumping factor 10) is very high for the spectral type, M˙ = 2.4 × 10−6 M⊙ a−1. The high rotational velocity and mass-loss rate place the star at the hot side of the bi-stability jump. Together with the nearly solar CNO abundance pattern, they may also point to evolution in a binary system, J20395358+4222505 being the initial secondary.SS-D and AH acknowledge support from the Spanish Government Ministerio de Ciencia e Innovación through grants PGC-2018-091 3741-B-C22 and CEX2019-000920-S and from the Canarian Agency for Research, Innovation and Information Society (ACIISI), of the Canary Islands Government, and the European Regional Development Fund (ERDF), under grant with reference ProID2020010016. MG and FN acknowledge financial support through Spanish grant PID2019-105552RB-C41 (MINECO/MCIU/AEI/FEDER) and from the Spanish State Research Agency (AEI) through the Unidad de Excelencia ‘María de Maeztu’-Centro de Astrobiología (CSIC-INTA) project No. MDM-2017-0737. SRB acknowledges support by the Spanish Government under grants AYA2015-68012-C2-2-P and PGC2018-093741-B-C21/C22 (MICIU/AEI/FEDER, UE). SRA acknowledges funding support from the FONDECYT Iniciación project 11171025 and the FONDECYT Regular project 1201490. JIP acknowledges finantial support from projects Estallidos6 AYA2016-79724-C4 (Spanish Ministerio de Economia y Competitividad), Estallidos7 PID2019-107408GB-C44 (Spanish Ministerio de Ciencia e Innovacion), grant P18-FR-2664 (Junta de Andalucía), and grant SEV-2017-0709 ‘Centro de Excelencia Severo Ochoa Program’ (Spanish Science Ministry). AGP, SP, AG-M, JG and NC acknowledge support from the Spanish MCI through project RTI2018-096188-B-I00