566 research outputs found
Accurate masses and radii of normal stars: modern results and applications
This paper presents and discusses a critical compilation of accurate,
fundamental determinations of stellar masses and radii. We have identified 95
detached binary systems containing 190 stars (94 eclipsing systems, and alpha
Centauri) that satisfy our criterion that the mass and radius of both stars be
known to 3% or better. To these we add interstellar reddening, effective
temperature, metal abundance, rotational velocity and apsidal motion
determinations when available, and we compute a number of other physical
parameters, notably luminosity and distance. We discuss the use of this
information for testing models of stellar evolution. The amount and quality of
the data also allow us to analyse the tidal evolution of the systems in
considerable depth, testing prescriptions of rotational synchronisation and
orbital circularisation in greater detail than possible before. The new data
also enable us to derive empirical calibrations of M and R for single (post-)
main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff),
log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.
Excellent agreement is found with independent determinations for host stars of
transiting extrasolar planets, and good agreement with determinations of M and
R from stellar models as constrained by trigonometric parallaxes and
spectroscopic values of T(eff) and [Fe/H]. Finally, we list a set of 23
interferometric binaries with masses known to better than 3%, but without
fundamental radius determinations (except alpha Aur). We discuss the prospects
for improving these and other stellar parameters in the near future.Comment: 56 pages including figures and tables. To appear in The Astronomy and
Astrophysics Review. Ascii versions of the tables will appear in the online
version of the articl
RC J0311+0507: A Candidate for Superpowerful Radio Galaxies in the Early Universe at Redshift z=4.514
A strong emission line at 6703A has been detected in the optical spectrum for
the host galaxy (R=23.1) of the radio source RC J0311+0507 (4C+04.11). This
radio galaxy, with a spectral index of 1.31 in the frequency range 365-4850
MHz, is one of the ultrasteep spectrum objects from the deep survey of a sky
strip conducted with RATAN-600 in 1980-1981. We present arguments in favor of
the identification of this line with Ly\alpha at redshift z=4.514. In this
case, the object belongs to the group of extremely distant radio galaxies of
ultrahigh radio luminosity (P_{1400}=1.3 x 10^{29}W Hz^{-1}). Such power can be
provided only by a fairly massive black hole (~10^9M_\sun}) that formed in a
time less than the age of the Universe at the observed z(1.3 Gyr) or had a
primordial origin.Comment: 8 pages, 3 figure
Three-year outcome after transanal versus laparoscopic total mesorectal excision in locally advanced rectal cancer : a multicenter comparative analysis
Altres ajuts: This work has been funded by the Resident Award "Emili Letang," granted by Hospital Clinic of Barcelona, Research, Innovation, and Education Departments (Grant number: 25_delacyoliverb_250709_cgicm_pfr2018). The funder of this study supported the data collection and database management.For patients with mid and distal rectal cancer, robust evidence on long-term outcome and causal treatment effects of transanal total mesorectal excision (TaTME) is lacking. This multicentre retrospective cohort study aimed to assess whether TaTME reduces locoregional recurrence rate compared to laparoscopic total mesorectal excision (LapTME). Consecutive patients with rectal cancer within 12 cm from the anal verge and clinical stage II-III were selected from three institutional databases. Outcome after TaTME (Nov 2011 - Feb 2018) was compared to a historical cohort of patients treated with LapTME (Jan 2000 - Feb 2018) using the inverse probability of treatment weights method. The primary endpoint was three-year locoregional recurrence. A total of 710 patients were analysed, 344 in the TaTME group and 366 in the LapTME group. At 3 years, cumulative locoregional recurrence rates were 3.6% (95% CI, 1.1-6.1) in the TaTME group and 9.6% (95% CI, 6.5-12.7) in the LapTME group (HR = 0.4; 95% CI, 0.23-0.69; p = 0.001). Three-year cumulative disease-free survival rates were 74.3% (95% CI, 68.8-79.8) and 68.6% (95% CI, 63.7-73.5) (HR = 0.82; 95% CI, 0.65-1.02; p = 0.078) and three-year overall survival 87.2% (95% CI, 82.7-91.7) and 82.2% (95% CI, 78.0-86.2) (HR = 0.74; 95% CI, 0.53-1.03; p = 0.077), respectively. In patients who underwent sphincter preservation procedures, TaTME was associated with a significantly better disease-free survival (HR = 0.78; 95% CI, 0.62-0.98; p = 0.033). These findings suggest that TaTME may improve locoregional recurrence and disease-free survival rates among patients with mid and distal locally advanced rectal cancer
Comparison of proactive and conventional treatment of anastomotic leakage in rectal cancer surgery:a multicentre retrospective cohort series
Purpose: Comparative studies on efficacy of treatment strategies for anastomotic leakage (AL) after low anterior resection (LAR) are almost non-existent. This study aimed to compare different proactive and conservative treatment approaches for AL after LAR. Methods: This retrospective cohort study included all patients with AL after LAR in three university hospitals. Different treatment approaches were compared, including a pairwise comparison of conventional treatment and endoscopic vacuum-assisted surgical closure (EVASC). Primary outcomes were healed and functional anastomosis rates at end of follow-up. Results: Overall, 103 patients were included, of which 59 underwent conventional treatment and 23 EVASC. Median number of reinterventions was 1 after conventional treatment, compared to 7 after EVASC (p < 0.01). Median follow-up was 39 and 25 months, respectively. Healed anastomosis rate was 61% after conventional treatment, compared to 78% after EVASC (p = 0.139). Functional anastomosis rate was higher after EVASC, compared to conventional treatment (78% vs. 54%, p = 0.045). Early initiation of EVASC in the first week after primary surgery resulted in better functional anastomosis rate compared to later initiation (100% vs. 55%, p = 0.008). Conclusion: Proactive treatment of AL consisting of EVASC resulted in improved healed and functional anastomosis rates for AL after LAR for rectal cancer, compared to conventional treatment. If EVASC was initiated within the first week after index surgery, a 100% functional anastomosis rate was achievable.</p
Comparison of proactive and conventional treatment of anastomotic leakage in rectal cancer surgery:a multicentre retrospective cohort series
Purpose: Comparative studies on efficacy of treatment strategies for anastomotic leakage (AL) after low anterior resection (LAR) are almost non-existent. This study aimed to compare different proactive and conservative treatment approaches for AL after LAR. Methods: This retrospective cohort study included all patients with AL after LAR in three university hospitals. Different treatment approaches were compared, including a pairwise comparison of conventional treatment and endoscopic vacuum-assisted surgical closure (EVASC). Primary outcomes were healed and functional anastomosis rates at end of follow-up. Results: Overall, 103 patients were included, of which 59 underwent conventional treatment and 23 EVASC. Median number of reinterventions was 1 after conventional treatment, compared to 7 after EVASC (p < 0.01). Median follow-up was 39 and 25 months, respectively. Healed anastomosis rate was 61% after conventional treatment, compared to 78% after EVASC (p = 0.139). Functional anastomosis rate was higher after EVASC, compared to conventional treatment (78% vs. 54%, p = 0.045). Early initiation of EVASC in the first week after primary surgery resulted in better functional anastomosis rate compared to later initiation (100% vs. 55%, p = 0.008). Conclusion: Proactive treatment of AL consisting of EVASC resulted in improved healed and functional anastomosis rates for AL after LAR for rectal cancer, compared to conventional treatment. If EVASC was initiated within the first week after index surgery, a 100% functional anastomosis rate was achievable.</p
CMB quenching of high-redshift radio-loud AGNs
The very existence of more than a dozen of high-redshift (z 73 4) blazars indicates that a much larger population of misaligned powerful jetted active galactic nucleus (AGN) was already in place when the Universe was 721.5 Gyr old. Such parent population proved to be very elusive, and escaped direct detection in radio surveys so far. High-redshift blazars themselves seem to be failing in producing extended radio lobes, raising questions about the connection between such class and the vaster population of radio galaxies. We show that the interaction of the jet electrons with the intense cosmic microwave background (CMB) radiation explains the lack of extended radio emission in high-redshift blazars and in their parent population, helping to explain the apparently missing misaligned counterparts of high-redshift blazars. On the other hand, the emission from the more compact and more magnetized hotspots are less affected by the enhanced CMB energy density. By modelling the spectral energy distribution of blazar lobes and hotspots, we find that most of them should be detectable by low-frequency deep radio observations, e.g. by LOw-Frequency ARray for radio astronomy and by relatively deep X-ray observations with good angular resolution, e.g. by the Chandra satellite. At high redshifts, the emission of a misaligned relativistic jet, being debeamed, is missed by current large sky area surveys. The isotropic flux produced in the hotspots can be below \u2dc1 mJy and the isotropic lobe radio emission is quenched by the CMB cooling. Consequently, even sources with very powerful jets can go undetected in current radio surveys, and misclassified as radio-quiet AGNs
Spitzer Observations of High Redshift Radio Galaxies
We present the results of a comprehensive Spitzer survey of 70 radio galaxies across 1 < z < 5.2. Using IRAC, IRS and MIPS imaging we determine the rest-frame AGN contribution to the stellar emission peak at 1.6μm. The stellar luminosities are found to be consistent with that of a giant elliptical with a stellar mass of 10^(11−12)M_⊙. The mean stellar mass remains constant at 10^(11.5)M_⊙ up to z = 3 indicating that the upper end of the mass function is already in place at redshift 3. The mid-IR luminosities imply bolometric IR luminosities that would classify most sources as ULIRGs. The mid-IR to radio luminosity generally correlate implying a common origin for these emissions. The ratio is higher than that found for lower redshift, i.e. z < 1, radio galaxies
Herschel-HIFI observations of high-J CO lines in the NGC 1333 low-mass star-forming region
Herschel-HIFI observations of high-J lines (up to J_u=10) of 12CO, 13CO and
C18O are presented toward three deeply embedded low-mass protostars, NGC 1333
IRAS 2A, IRAS 4A, and IRAS 4B, obtained as part of the Water In Star-forming
regions with Herschel (WISH) key program. The spectrally-resolved HIFI data are
complemented by ground-based observations of lower-J CO and isotopologue lines.
The 12CO 10-9 profiles are dominated by broad (FWHM 25-30 km s^-1) emission.
Radiative transfer models are used to constrain the temperature of this shocked
gas to 100-200 K. Several CO and 13CO line profiles also reveal a medium-broad
component (FWHM 5-10 km s^-1), seen prominently in H2O lines. Column densities
for both components are presented, providing a reference for determining
abundances of other molecules in the same gas. The narrow C18O 9-8 lines probe
the warmer part of the quiescent envelope. Their intensities require a jump in
the CO abundance at an evaporation temperature around 25 K, thus providing new
direct evidence for a CO ice evaporation zone around low-mass protostars.Comment: 8 pages, 9 figure
Spectroscopy of Ultra Steep Spectrum Radio Sources
We present optical spectroscopy of 62 objects selected from several samples
of ultra steep spectrum (USS) radio sources. 46 of these are from our primary
catalog, consisting of 669 sources with radio spectral indices alpha < -1.30
(S_nu ~ nu^alpha); this first spectroscopic sub-sample was selected on the
basis of their faint optical and near-IR identifications. Most are identified
as narrow-lined radio galaxies with redshifts ranging from z=0.25 to z=5.19.
Ten objects are at z>3, nearly doubling the number of such sources known to
date. Four of the USS radio sources are identified with quasars, of which at
least three have very red spectral energy distributions. The source TN
J0936-2242 is identified with an extremely red object (ERO, R-K>5); both it and
a close companion are at z=1.479. The spectrum of the ERO closely resembles
that of previously discovered radio galaxies at z~1.5. Five sources show
continuum emission, but fail to show any clear emission or absorption features,
despite integrations of ~1 h with the Keck telescope. We suggest that these
objects could be (i) radio galaxies with faint emission lines in the ``redshift
desert'' at 1.5 <~ z <~ 2.3, (ii) radio galaxies with an obscured AGN, which
are dominated by a stellar continuum observed with insufficient S/N, or (iii)
pulsars. Three radio sources identified with faint objects in the K-band images
remain undetected in 50-90 min spectroscopic integrations with the Keck
telescope, and are possible z>7 candidates.Comment: 59 Pages, including 59 PostScript figures. Accepted for publication
in the Astronomical Journal (March 2001 issue). Tables 5 and 6 will be
available in electronic format on the AJ website or upon reques
Identifying Luminous AGN in Deep Surveys: Revised IRAC Selection Criteria
Spitzer IRAC selection is a powerful tool for identifying luminous AGN. For
deep IRAC data, however, the AGN selection wedges currently in use are heavily
contaminated by star-forming galaxies, especially at high redshift. Using the
large samples of luminous AGN and high-redshift star-forming galaxies in
COSMOS, we redefine the AGN selection criteria for use in deep IRAC surveys.
The new IRAC criteria are designed to be both highly complete and reliable, and
incorporate the best aspects of the current AGN selection wedges and of
infrared power-law selection while excluding high redshift star-forming
galaxies selected via the BzK, DRG, LBG, and SMG criteria. At QSO-luminosities
of log L(2-10 keV) (ergs/s) > 44, the new IRAC criteria recover 75% of the hard
X-ray and IRAC-detected XMM-COSMOS sample, yet only 38% of the IRAC AGN
candidates have X-ray counterparts, a fraction that rises to 52% in regions
with Chandra exposures of 50-160 ks. X-ray stacking of the individually X-ray
non-detected AGN candidates leads to a hard X-ray signal indicative of heavily
obscured to mildly Compton-thick obscuration (log N_H (cm^-2) = 23.5 +/- 0.4).
While IRAC selection recovers a substantial fraction of luminous unobscured and
obscured AGN, it is incomplete to low-luminosity and host-dominated AGN.Comment: 22 pages, 15 figures, accepted for publication in ApJ, full
resolution version available at http://www.stsci.edu/~donley/iragn_paper
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