While most of the known debris discs present cold dust at tens of astronomical unit (au), a few young systems exhibit hot dust analogous to the Zodiacal dust. ... Corvi is particularly interesting as ...it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here, we present ALMA observations of ... Corvi with a resolution of 1.2 arcsec (~22 au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152 au and radial full width at half-maximum of 46 au, which is too narrow compared to models of inward scattering of an LHB-like scenario. Instead, the hot dust could be explained as material passed inwards in a rather stable planetary configuration. We also report a 4s detection of CO at ~20 au. CO could be released in situ from icy planetesimals being passed in when crossing the H2O or CO2 ice lines. Finally, we place constraints on hidden planets in the disc. If a planet is sculpting the disc's inner edge, this should be orbiting at 75-100 au, with a mass of 3-30 M... and an eccentricity <0.08. Such a planet would be able to clear its chaotic zone on a time-scale shorter than the age of the system and scatter material inwards from the outer belt to the inner regions, thus feeding the hot dust. (ProQuest: ... denotes formulae/symbols omitted.)
In recent years, gas has been observed in an increasing number of debris discs, though its nature remains to be determined. Here, we analyse CO molecular excitation in optically thin debris discs, ...and search Atacama Large Millimeter/submillimeter Array (ALMA) Cycle-0 data for CO J = 3-2 emission in the Fomalhaut ring. No significant line emission is observed; we set a 3... upper limit on the integrated line flux of 0.16 Jy km s... We show a significant dependence of the CO excitation on the density of collisional partners n, on the gas kinetic temperature T... and on the ambient radiation field J, suggesting that assumptions widely used for protoplanetary discs (e.g. local thermodynamic equilibrium, LTE) do not necessarily apply to their low density debris counterparts. When applied to the Fomalhaut ring, we consider a primordial origin scenario where H... dominates collisional excitation of CO, and a secondary origin scenario dominated by e- and H...O. In either scenario, we obtain a strict upper limit on the CO mass of 4.9 x 10... M... This arises in the non-LTE regime, where the excitation of the molecule is determined solely by the well-known radiation field. In the secondary scenario, assuming any CO present to be in steady state allows us to set an upper limit of ~55 per cent on the CO/H...O ice ratio in the parent planetesimals. This could drop to ~3 per cent if LTE applies, covering the range observed in Solar system comets (0.4-30 per cent). Finally, in light of our analysis, we present prospects for CO detection and characterization in debris discs with ALMA. (ProQuest: ... denotes formulae/symbols omitted.)
Recent ALMA observations unveiled the structure of CO gas in the 23 Myr old beta Pictoris planetary system, a component that has been discovered in many similarly young debris discs. We here present ...ALMA CO J = 2-1 observations, at an improved spectro-spatial resolution and sensitivity compared to previous CO J = 3-2 observations. We find that (1) the CO clump is radially broad, favouring the resonant migration over the giant impact scenario for its dynamical origin, (2) the CO disc is vertically tilted compared to the main dust disc, at an angle consistent with the scattered light warp. We then use position-velocity diagrams to trace Keplerian radii in the orbital plane of the disc. Assuming a perfectly edge-on geometry, this shows a CO scaleheight increasing with radius as R super( 0.75), and an electron density derived from CO line ratios through non-local thermodynamic equilibrium (NLTE) analysis in agreement with thermodynamical models. Furthermore, we show how observations of optically thin line ratios can solve the primordial versus secondary origin dichotomy in gas-bearing debris discs. As shown for beta Pictoris, subthermal (NLTE) CO excitation is symptomatic of H sub( 2) densities that are insufficient to shield CO from photodissociation over the system's lifetime. This means that replenishment from exocometary volatiles must be taking place, proving the secondary origin of the disc. In this scenario, assuming steady state production/destruction of CO gas, we derive the CO+CO sub( 2) ice abundance by mass in beta Pic's exocomets to be at most ~6 per cent, consistent with comets in our own Solar system and in the coeval HD181327 system.
While most of the known debris discs present cold dust at tens of astronomical unit (au), a few young systems exhibit hot dust analogous to the Zodiacal dust. ... Corvi is particularly interesting as ...it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here, we present ALMA observations of ... Corvi with a resolution of 1.2 arcsec (~22 au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152 au and radial full width at half-maximum of 46 au, which is too narrow compared to models of inward scattering of an LHB-like scenario. Instead, the hot dust could be explained as material passed inwards in a rather stable planetary configuration. We also report a 4s detection of CO at ~20 au. CO could be released in situ from icy planetesimals being passed in when crossing the H2O or CO2 ice lines. Finally, we place constraints on hidden planets in the disc. If a planet is sculpting the disc's inner edge, this should be orbiting at 75-100 au, with a mass of 3-30 M... and an eccentricity <0.08. Such a planet would be able to clear its chaotic zone on a time-scale shorter than the age of the system and scatter material inwards from the outer belt to the inner regions, thus feeding the hot dust. (ProQuest: ... denotes formulae/symbols omitted.)
Recent ALMA observations unveiled the structure of CO gas in the 23 Myr old β Pictoris planetary system, a component that has been discovered in many similarly young debris discs. We here present ...ALMA CO J = 2-1 observations, at an improved spectro-spatial resolution and sensitivity compared to previous CO J = 3-2 observations. We find that (1) the CO clump is radially broad, favouring the resonant migration over the giant impact scenario for its dynamical origin, (2) the CO disc is vertically tilted compared to the main dust disc, at an angle consistent with the scattered light warp. We then use position-velocity diagrams to trace Keplerian radii in the orbital plane of the disc. Assuming a perfectly edge-on geometry, this shows a CO scaleheight increasing with radius as R^sup 0.75^, and an electron density derived from CO line ratios through non-local thermodynamic equilibrium (NLTE) analysis in agreement with thermodynamical models. Furthermore, we show how observations of optically thin line ratios can solve the primordial versus secondary origin dichotomy in gas-bearing debris discs. As shown for β Pictoris, subthermal (NLTE) CO excitation is symptomatic of H^sub 2^ densities that are insufficient to shield CO from photodissociation over the system's lifetime. This means that replenishment from exocometary volatiles must be taking place, proving the secondary origin of the disc. In this scenario, assuming steady state production/destruction of CO gas, we derive the CO+CO^sub 2^ ice abundance by mass in β Pic's exocomets to be at most ~6 per cent, consistent with comets in our own Solar system and in the coeval HD181327 system.
Indirect detections of massive - presumably Jupiter-like - planets orbiting nearby Sun-like stars have recently been reported,. Rocky, Earth-like planets are much more difficult to detect, but clues ...to their possible existence can nevertheless be obtained from observations of the circumstellar debris disks of dust from which they form. The presence of such disks has been inferred from excess far-infrared emission but, with the exception of β Pictoris, it has proved difficult to image these structures directly as starlight dominates the faint light scattered by the dust. A more promising approach is to attempt to image the thermal emission from the dust grains at submillimetre wavelengths,. Here we present images of such emission around Fomalhaut, β Pictoris and Vega. For each star, dust emission is detected from regions comparable in size to the Sun's Kuiper belt of comets. The total dust mass surrounding each star is only a few lunar masses, so any Earth-like planets present must already have formed. The presence of the central cavity, approximately the size of Neptune's orbit, that we detect in the emission from Fomalhaut may indeed be the signature of such planets.
Spectra obtained from ground-based radio telescopes show the progressive release of CO, CH$_3$OH, HCN, H$_2$O (from OH), H$_2$S, CS, H$_2$CO, CH$_3$CN, and HNC as comet Hale-Bopp (C/1995 01) ...approached the sun from 6.9 to 1.4 astronomical units (AU). The more volatile species were relatively more abundant in the coma far from the sun, but there was no direct correlation between overabundance and volatility. Evidence for H$_2$O sublimation from icy grains was seen beyond 3.5 AU from the sun. The change from a CO-driven coma to an H$_2$O-driven coma occurred at about 3 AU. The gas outflow velocity and temperature increased as Hale-Bopp approached the sun.
(1) Safety and monitoring should be part of a quality assurance programme for endoscopy units. (2) Resuscitation equipment and drugs must be available in the endoscopy and recovery areas. (3) Staff ...of all grades and disciplines should be familiar with resuscitation methods and undergo periodic retraining. (4) Equipment and drugs necessary for the maintenance of airway, breathing, and circulation should be present in the endoscopy unit and recovery area (if outside the unit) and checked regularly. (5) A qualified nurse, trained in endoscopic techniques and adequately trained in resuscitation techniques, should monitor the patient's condition during procedures. (6) Before endoscopy, adverse risk factors should be identified. This may be aided by the use of a check list. (7) The dosage of all drugs should be kept to the minimum necessary. There is evidence that benzodiazepine/opioid mixtures are hazardous. (8) Specific antagonists for benzodiazepines and opioids exist and should be available in the event of emergency. (9) A cannula should be placed in a vein during endoscopy on 'at risk' patients. (10) Oxygen enriched air should be given to 'at risk' patients undergoing endoscopic procedures. (11) The endoscopist should ensure the well being and clinical observation of the patient undergoing endoscopy in conjunction with another individual. This individual should be a qualified nurse trained in endoscopic techniques or another medically qualified practitioner. (12) Monitoring techniques such as pulse oximetry are recommended. (13) Clinical monitoring of the patient must be continued into the recovery area. (14) Records of management and outcome should be collected and will provide data for appropriate audit.
Extrasolar Analogues to the Kuiper Belt Wyatt, Mark C.; Holland, Wayne S.; Greaves, Jane S. ...
Earth, moon, and planets,
06/2003, Letnik:
92, Številka:
1-4
Journal Article
Debris disks are found around some 15% of main sequencestars and their dust is thought to be continuallyreplenished in collisions between planetesimals inextrasolar Kuiper belts.While they were ...discovered in 1984 by IRAS, it is onlywith more recent imaging that their true nature has beenrevealed. This paper discusses recent debris disk images andtheir impact on our understanding of extrasolar systems.Importantly these images confirm the extrasolar Kuiper belthypothesis for most (but not all) debris diskcandidates and show that the planetesimals within thesedisks must have grown to at least a few km.Asymmetries in imaged disk structures also provide informationabout the planetary systems orbiting inside these planetesimalbelts. The impact of debris disk studies on our understandingof the evolution of our own Kuiper belt, as well as theirpotential to solve puzzles such as the origin of the missingmass and the outer edge of the Kuiper belt, is alsodiscussed.
Methotrexate (MTX) has become an important drug in the treatment of rheumatoid arthritis (RA). The American College of Rheumatology convened a committee to assess the risks of development of ...clinically significant liver disease (CSLD) during MTX treatment, to evaluate the risk and role of surveillance liver biopsies, and to provide recommendations about monitoring patients for liver toxicity. The committee recommends obtaining liver blood tests (alanine aminotransferase ALT, aspartate aminotransferase AST, alkaline phosphatase, albumin, bilirubin), hepatitis B and C serologic studies, and other standard tests including complete blood cell count and serum creatinine tests prior to starting treatment with MTX. A pretreatment liver biopsy should be considered only for patients with a history of prior excessive alcohol consumption, persistently abnormal baseline AST values, or chronic hepatitis B or C infection. At intervals of every 4-8 weeks the AST, ALT, and albumin levels should be monitored. Routine surveillance liver biopsies are not recommended for RA patients receiving traditional doses of MTX. However, a biopsy should be performed if a patient develops persistent abnormalities on liver blood tests. These are defined as elevations (above the upper limit of laboratory normal) in the AST in 5 of 9 determinations within a given 12-month interval (6 of 12 if tests are performed monthly) or a decrease in serum albumin below the normal range. The recommendations for monitoring and selection of patients for liver biopsy identify patients at potential risk for CSLD, and thus significantly reduce the number of patients who would be exposed to this procedure. Close monitoring is essential to reduce the risk of unrecognized serious liver disease. These recommendations should be revised as necessary to reflect new and compelling information. (DBO)
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