1,578 research outputs found
HH 1158: The lowest luminosity externally irradiated Herbig-Haro jet
We have identified a new externally irradiated Herbig-Haro (HH) jet, HH 1158,
within ~2 pc of the massive OB type stars in the sigma Orionis cluster. At an
Lbol ~ 0.1 Lsun, HH 1158 is the lowest luminosity irradiated HH jet identified
to date in any cluster. Results from the analysis of high-resolution optical
spectra indicate asymmetries in the brightness, morphology, electron density,
velocity, and the mass outflow rates for the blue and red-shifted lobes. We
constrain the position angle of the HH 1158 jet at 102+/-5 degree. The mass
outflow rate and the mean accretion rate for HH 1158 using multiple diagnostics
are estimated to be (5.2 +/- 2.6) x 10^(-10) Msun/yr and (3.0 +/- 1.0) x
10^(-10) Msun/yr, respectively. The properties for HH 1158 are notably similar
to the externally irradiated HH 444 -- HH 447 jets previously identified in
sigma Orionis. In particular, the morphology is such that the weaker jet beam
is tilted towards the massive stars, indicating a higher extent of
photo-evaporation. The high value for the Halpha/[SII] ratio is also consistent
with the ratios measured in other irradiated jets, including HH 444 -- HH 447.
The presence of an extended collimated jet that is bipolar and the evidence of
shocked emission knots make HH 1158 the first unique case of irradiated HH jets
at the very low-luminosity end, and provides an opportunity to learn the
physical properties of very faint HH jet sources.Comment: Accepted in ApJ Letter
Chemical tracers in proto-brown dwarfs: CO, ortho-HCO, para-HCO, HCO, CS observations
We present a study of the CO isotopologues and the high-density tracers
HCO, HCO, and CS in Class 0/I proto-brown dwarfs (proto-BDs). We
have used the IRAM 30m telescope to observe the CO (2-1), CO
(2-1), CO (2-1), CO (2-1), HCO (3-2), HCO (3-2), and
CS (5-4) lines in 7 proto-BDs. The hydrogen column density for the proto-BDs
derived from the CO gas emission is 2-15 times lower than that derived
from the dust continuum emission, indicating CO depletion from the gas-phase.
The mean HCO ortho-to-para ratio is 3 for the proto-BDs and
indicates gas-phase formation for HCO. We have investigated the
correlations in the molecular abundances between the proto-BDs and protostars.
Proto-BDs on average show a factor of 2 higher ortho-to-para HCO
ratio than the protostars. Possible explanations include a difference in the
HCO formation mechanism, spin-selective photo-dissociation,
self-shielding effects, or different emitting regions for the ortho and para
species. There is a tentative trend of a decline in the HCO and HCO
abundances with decreasing bolometric luminosity, while the CS and CO
abundances show no particular difference between the proto-BDs and protostars.
These trends reflect the scaled-down physical structures for the proto-BDs
compared to protostars and differences in the peak emitting regions for these
species. The CO isotopologue is detected in all of the proto-BDs as well
as the more evolved Class Flat/Class II BDs in our sample, and can probe the
quiescent gas at both early and late evolutionary stages.Comment: Accepted in MNRAS. arXiv admin note: text overlap with
arXiv:1809.1016
Chemical tracers in proto-brown dwarfs: CN, HCN, and HNC observations
We present results from a study of nitrogen chemistry in Class 0/I
proto-brown dwarfs (proto-BDs). We have used the IRAM 30 m telescope to observe
the CN (2-1), HCN (3-2), and HNC (3-2) lines in 7 proto-BDs. All proto-BDs show
a large CN/HCN abundance ratio of >20, and a HNC/HCN abundance ratio close to
or larger than unity. The enhanced CN/HCN ratios can be explained by high UV
flux originating from an active accretion zone in the proto-BDs. The larger
than unity HNC/HCN ratio for the proto-BDs is likely caused by a combination of
low temperature and high density. Both CN and HNC show a flat distribution with
CO, indicating that these species can survive in regions where CO is depleted.
We have investigated the correlations in the molecular abundances of these
species for the proto-BDs with Class 0/I protostars. We find tentative trends
of CN (HCN) abundances being about an order of magnitude higher (lower) in the
proto-BDs compared to protostars. HNC for the proto-BDs shows a nearly constant
abundance unlike the large spread of ~2 orders of magnitude seen for the
protostars. Also notable is a rise in the HNC/HCN abundance ratio for the
lowest luminosity objects, suggesting that this ratio is higher under
low-temperature environments. None of the relatively evolved Class Flat/Class
II brown dwarfs in our sample show emission in HNC. The HNC molecule can be
considered as an efficient tracer to search and identify early stage
sub-stellar mass objects.Comment: Accepted in MNRA
Herschel PACS and SPIRE Observations of TWA brown dwarf discs
We present Herschel SPIRE observations for the TW Hydrae association (TWA)
brown dwarf discs SSSPM J1102-3431 (SS1102) and 2MASSW J1207334-393254
(2M1207). Both discs are undetected in the SPIRE 200-500mu bands. We have also
analyzed the archival PACS data and find no detection for either source in the
160mu band. Based on radiative transfer modeling, we estimate an upper limit to
the disc mass for both sources of 0.1 M_Jup. The lack of detection in the SPIRE
bands could be due to a paucity of millimeter sized dust grains in the 2M1207
and SS1102 discs. We also report a non-detection for the brown dwarf 2MASS
J1139511-315921 (2M1139) in the PACS 70 and 160mu bands. We have argued for the
presence of a warm debris disc around 2M1139, based on an excess emission
observed at 24mu. The mid-infrared colors for 2M1139 are similar to the
transition discs in the Taurus and Ophuichus regions. A comparison of the brown
dwarf disc masses over a ~1-10 Myr age interval suggests a decline in the disc
mass with the age of the system.Comment: Accepted in A&
Revised analysis of SPIRE observations for 2M1207
We have revised our analysis of the SPIRE observations of 2MASSW
J1207334-393254 (2M1207). Recent PACS observations show a bright source located
~25" east of 2M1207. There are issues in terms of the detection/non-detection
of the bright source when comparing the Spitzer, WISE, and PACS observations.
It is apparently inconsistent, perhaps due to variability or low
signal-to-noise of the data. We have looked into the possible misidentification
of the target, and have revised the measured SPIRE fluxes and the disc
parameters for 2M1207. We have also reviewed which among the various formation
mechanisms of this system would still be valid.Comment: Revised SPIRE fluxe
A near-infrared variability campaign of TMR-1: New light on the nature of the candidate protoplanet TMR-1C
(abridged) We present a near-infrared (NIR) photometric variability study of
the candidate protoplanet, TMR-1C, located at a separation of about 10" (~1000
AU) from the Class I protobinary TMR-1AB in the Taurus molecular cloud. Our
campaign was conducted between October, 2011, and January, 2012. We were able
to obtain 44 epochs of observations in each of the H and Ks filters. Based on
the final accuracy of our observations, we do not find any strong evidence of
short-term NIR variability at amplitudes of >0.15-0.2 mag for TMR-1C or
TMR-1AB. Our present observations, however, have reconfirmed the
large-amplitude long-term variations in the NIR emission for TMR-1C, which were
earlier observed between 1998 and 2002, and have also shown that no particular
correlation exists between the brightness and the color changes. TMR-1C became
brighter in the H-band by ~1.8 mag between 1998 and 2002, and then fainter
again by ~0.7 mag between 2002 and 2011. In contrast, it has persistently
become brighter in the Ks-band in the period between 1998 and 2011. The (H-Ks)
color for TMR-1C shows large variations, from a red value of 1.3+/-0.07 and
1.6+/-0.05 mag in 1998 and 2000, to a much bluer color of -0.1+/-0.5 mag in
2002, and then again a red color of 1.1+/-0.08 mag in 2011. The observed
variability from 1998 to 2011 suggests that TMR-1C becomes fainter when it gets
redder, as expected from variable extinction, while the brightening observed in
the Ks-band could be due to physical variations in its inner disk structure.
The NIR colors for TMR-1C obtained using the high precision photometry from
1998, 2000, and 2011 observations are similar to the protostars in Taurus,
suggesting that it could be a faint dusty Class I source. Our study has also
revealed two new variable sources in the vicinity of TMR-1AB, which show
long-term variations of ~1-2 mag in the NIR colors between 2002 and 2011.Comment: Accepted in A&
New Brown Dwarf Disks in the TW Hydrae Association
In our analysis of {\it Spitzer}/IRS archival data on the stellar and
sub-stellar members of the TW Hydrae Association (TWA), we have discovered two
new brown dwarf disks: a flat optically thick disk around SSSPM J1102-3431
(SSSPM 1102), and a transition disk around 2MASS J1139511-315921 (2M1139). The
disk structure for SSSPM 1102 is found to be very similar to the known brown
dwarf disk 2MASSW J1207334-393254 (2M1207), with excess emission observed at
wavelengths as short as 5 \micron. 2M1139 shows no excess emission shortward
of 20 \micron, but flares up at longer wavelengths, and is the first
transition disk detected among the sub-stellar members of TWA. We also report
on the {\it Spitzer}/70 \micron observations, and the presence of a weak {\it
absorption} 10 \micron silicate feature for 2M1207. The absorption can be
attributed to a close to edge-on disk at a 75\degr inclination. The 10
\micron spectrum for 2M1207 shows crystalline forsterite features, with a
peak in absorption near 11.3 \micron. No silicate absorption/emission is
observed towards SSSPM 1102. While only 6 out of 25 stellar members show excess
emission at these mid-infrared wavelengths, {\it all} of the TWA brown dwarfs
that have been observed so far with {\it Spitzer} show signs of disks around
them, resulting in a disk fraction of at least 60%. This is a considerable
fraction at a relatively older age of 10 Myr. A comparison with younger
clusters indicates that by the age of the TWA (10 Myr), the disk fraction
for brown dwarfs has not decreased, whereas it drops by a factor of 2 for
the higher mass stars. This suggests longer disk decay time scales for brown
dwarfs compared to higher mass stars.Comment: 23 pages, 6 figures. Accepted in Ap
Testing Regular Black Holes with X-ray data of GX~339--4
Regular black holes are singularity-free black hole spacetimes proposed to
solve the problem of the presence of spacetime singularities that plagues the
black holes of general relativity and most theories of gravity. In this work,
we consider the regular black holes recently proposed by Mazza, Franzin \&
Liberati and we extend previous studies to get a more stringent observational
constraint on the regularization parameter . We study simultaneous
observations of \textit{NuSTAR} and \textit{Swift} of the Galactic black hole
in GX~339--4 during its outburst in 2015. The quality of the \textit{NuSTAR}
data is exceptionally good and the spectrum of the source presents both a
strong thermal component and prominent relativistically blurred reflection
features. This permits us to measure the regularization parameter from the
simultaneous analysis of the thermal spectrum and the reflection features. From
our analysis, we find the constraint (90\% CL), which is stronger
than previous constraints inferred with X-ray and gravitational wave data
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