Context.
The Centaur (10199) Chariklo has the first ring system discovered around a small object. It was first observed using stellar occultation in 2013. Stellar occultations allow sizes and shapes ...to be determined with kilometre accuracy, and provide the characteristics of the occulting object and its vicinity.
Aims.
Using stellar occultations observed between 2017 and 2020, our aim is to constrain the physical parameters of Chariklo and its rings. We also determine the structure of the rings, and obtain precise astrometrical positions of Chariklo.
Methods.
We predicted and organised several observational campaigns of stellar occultations by Chariklo. Occultation light curves were measured from the datasets, from which ingress and egress times, and the ring widths and opacity values were obtained. These measurements, combined with results from previous works, allow us to obtain significant constraints on Chariklo’s shape and ring structure.
Results.
We characterise Chariklo’s ring system (C1R and C2R), and obtain radii and pole orientations that are consistent with, but more accurate than, results from previous occultations. We confirm the detection of W-shaped structures within C1R and an evident variation in radial width. The observed width ranges between 4.8 and 9.1 km with a mean value of 6.5 km. One dual observation (visible and red) does not reveal any differences in the C1R opacity profiles, indicating a ring particle size larger than a few microns. The C1R ring eccentricity is found to be smaller than 0.022 (3
σ
), and its width variations may indicate an eccentricity higher than ~0.005. We fit a tri-axial shape to Chariklo’s detections over 11 occultations, and determine that Chariklo is consistent with an ellipsoid with semi-axes of 143.8
−1.5
+1.4
, 135.2
−2.8
+1.4
, and 99.1
−2.7
+5.4
km. Ultimately, we provided seven astrometric positions at a milliarcsecond accuracy level, based on
Gaia
EDR3, and use it to improve Chariklo’s ephemeris.
Context.
Stellar occultations have become one of the best techniques to gather information about the physical properties of trans-Neptunian objects (TNOs), which are critical objects for ...understanding the origin and evolution of our Solar System.
Aims.
The purpose of this work is to determine, with better accuracy, the physical characteristics of the TNO (84922) 2003 VS
2
through the analysis of the multichord stellar occultation on 2019 October 22 and photometric data collected afterward.
Methods.
We predicted, observed, and analyzed the multichord stellar occultation of the Second
Gaia
Data Release
(Gaia
DR2) source 3449076721168026624
(m
υ
= 14.1 mag) by the plutino object 2003 VS
2
on 2019 October 22. We performed aperture photometry on the images collected and derived the times when the star disappeared and reappeared from the observing sites that reported a positive detection. We fit the extremities of such positive chords to an ellipse using a Monte Carlo method. We also carried out photometric observations to derive the rotational light curve amplitude and rotational phase of 2003 VS2 during the stellar occultation. Combining the results and assuming a triaxial shape, we derived the 3D shape of 2003 VS2.
Results.
Out of the 39 observatories involved in the observational campaign, 12 sites, located in Bulgaria (one), Romania (ten), and Serbia (one), reported a positive detection; this makes it one of the best observed stellar occultations by a TNO so far. Considering the rotational phase of 2003 VS
2
during the stellar occultation and the rotational light curve amplitude derived (Am = 0.264 ± 0.017 mag), we obtained a mean area-equivalent diameter of
D
Aeq
= 545 ± 13 km and a geometric albedo of 0.134 ± 0.010. By combining the rotational light curve information with the stellar occultation results, we derived the best triaxial shape for 2003 VS2, which has semiaxes
a
= 339 ± 5 km,
b
= 235 ± 6 km, and
c
= 226 ± 8 km. The derived aspect angle of 2003 VS
2
is
θ
= 59
°
± 2
°
or its supplementary
θ
= 121
°
± 2
°
, depending on the north-pole position of the TNO. The spherical-volume equivalent diameter is
D
Veq
= 524 ± 7 km. If we consider large albedo patches on its surface, the semi-major axis of the ellipsoid could be ~ 10 km smaller. These results are compatible with the previous ones determined from the single-chord 2013 and four-chord 2014 stellar occultations and with the effective diameter and albedo derived from
Herschel
and
Spitzer
data. They provide evidence that 2003 VS
2
’s 3D shape is not compatible with a homogeneous triaxial body in hydrostatic equilibrium, but it might be a differentiated body and/or might be sustaining some stress. No secondary features related to rings or material orbiting around 2003 VS2 were detected.
ABSTRACT
We predicted a stellar occultation of the bright star Gaia DR1 4332852996360346368 (UCAC4 385-75921) (mV = 14.0 mag) by the centaur 2002 GZ32 for 2017 May 20. Our latest shadow path ...prediction was favourable to a large region in Europe. Observations were arranged in a broad region inside the nominal shadow path. Series of images were obtained with 29 telescopes throughout Europe and from six of them (five in Spain and one in Greece) we detected the occultation. This is the fourth centaur, besides Chariklo, Chiron, and Bienor, for which a multichord stellar occultation is reported. By means of an elliptical fit to the occultation chords, we obtained the limb of 2002 GZ32 during the occultation, resulting in an ellipse with axes of 305 ± 17 km × 146 ± 8 km. From this limb, thanks to a rotational light curve obtained shortly after the occultation, we derived the geometric albedo of 2002 GZ32 (pV = 0.043 ± 0.007) and a 3D ellipsoidal shape with axes 366 km × 306 km × 120 km. This shape is not fully consistent with a homogeneous body in hydrostatic equilibrium for the known rotation period of 2002 GZ32. The size (albedo) obtained from the occultation is respectively smaller (greater) than that derived from the radiometric technique but compatible within error bars. No rings or debris around 2002 GZ32 were detected from the occultation, but narrow and thin rings cannot be discarded.
Abstract
Background
It has been suggested that biologic therapy may increase the risk of postoperative complications in inflammatory bowel disease (IBD), but the evidence is scarce. Our aim was to ...evaluate whether the treatment with anti-TNF agents, ustekinumab or vedolizumab increase the risk of complications after surgery.
Methods
IBD patients undergoing intra-abdominal surgery between 1st January 2009 and 31st December of 2019 were retrospectively selected. Data collection included clinical characteristic of IBD, biochemical parameters and surgical aspects. Postoperative complications (PC) were defined as those occurring within 30 days after surgery. Exposed cohort (EC): Patients who received the last dose of the biologic within 3 months before surgery. Non-exposed cohort (NEC): Patients who did not receive biologic treatment within 3 moths prior to surgery. Predictive factors for PC and for infections were identified by logistic regression analyses. A genetic matching score was performed to balance the clinical characteristics of both groups.
Results
A total of 1,535 surgeries performed in 37 centres were included: 81% in Crohn’s disease, 18% in ulcerative colitis and 1% in unclassified-IBD patients. A total of 711 surgeries (46.3%) had been exposed to biologics (583 under anti-TNF therapy, 58 under vedolizumab and 69 under ustekinumab) and 824 surgeries (53.7%) the NEC. PC were reported in 38% (n=267) of patients in the exposed cohort and in 34% (n=280) of patients in the non-exposed one (p=0.15), including dehiscence, infection, obstruction, ileus, bleeding, thrombosis, fistula and evisceration. The most frequent complications were infections (48% of all the cases). A 30-day hospital readmission was needed in 7% (n=110) of the patients, and 2% (n=29) required a new surgery with no differences (p>0.05). Multivariate analysis for PC and infections is presented in table 1. The frequencies of PC for each biologic in the univariate analysis are represented in figure 1. No specific treatment was associated to PC or infections in multivariate analysis.
Conclusion
Preoperative administration of biological therapy does not seem to be a risk factor for overall PC, although it may be for postoperative infections.
Context.
Trans-Neptunian objects (TNOs) and Centaurs are remnants of our planetary system formation, and their physical properties have invaluable information for evolutionary theories. Stellar ...occultation is a ground-based method for studying these distant small bodies and has presented exciting results. These observations can provide precise profiles of the involved body, allowing an accurate determination of its size and shape.
Aims.
The goal is to show that even single-chord detections of TNOs allow us to measure their milliarcsecond astrometric positions in the reference frame of the
Gaia
second data release (DR2). Accurate ephemerides can then be generated, allowing predictions of stellar occultations with much higher reliability.
Methods.
We analyzed data from various stellar occultation detections to obtain astrometric positions of the involved bodies. The events published before the
Gaia
era were updated so that the
Gaia
DR2 stellar catalog is the reference, thus providing accurate positions. Events with detection from one or two different sites (single or double chord) were analyzed to determine the event duration. Previously determined sizes were used to calculate the position of the object center and its corresponding error with respectto the detected chord and the International Celestial Reference System propagated
Gaia
DR2 star position.
Results.
We derive 37 precise astrometric positions for 19 TNOs and four Centaurs. Twenty-one of these events are presented here for the first time. Although about 68% of our results are based on single-chord detection, most have intrinsic precision at the submilliarcsecond level. Lower limits on the diameter of bodies such as Sedna, 2002 KX
14
, and Echeclus, and also shape constraints on 2002 VE
95
, 2003 FF
128
, and 2005 TV
189
are presented as valuable byproducts.
Conclusions.
Using the
Gaia
DR2 catalog, we show that even a single detection of a stellar occultation allows improving the object ephemeris significantly, which in turn enables predicting a future stellar occultation with high accuracy. Observational campaigns can be efficiently organized with this help, and may provide a full physical characterization of the involved object, or even the study of topographic features such as satellites or rings.
Context.
Deriving physical properties of trans-Neptunian objects is important for the understanding of our Solar System. This requires observational efforts and the development of techniques suitable ...for these studies.
Aims.
Our aim is to characterize the large trans-Neptunian object (TNO) 2002 TC
302
.
Methods.
Stellar occultations offer unique opportunities to determine key physical properties of TNOs. On 28 January 2018, 2002 TC
302
occulted a
m
v
~ 15.3 star with designation 593-005847 in the UCAC4 stellar catalog, corresponding to
Gaia
source 130957813463146112. Twelve positive occultation chords were obtained from Italy, France, Slovenia, and Switzerland. Also, four negative detections were obtained near the north and south limbs. This represents the best observed stellar occultation by a TNO other than Pluto in terms of the number of chords published thus far. From the 12 chords, an accurate elliptical fit to the instantaneous projection of the body can be obtained that is compatible with the near misses.
Results.
The resulting ellipse has major and minor axes of 543 ± 18 km and 460 ± 11 km, respectively, with a position angle of 3 ± 1 degrees for the minor axis. This information, combined with rotational light curves obtained with the 1.5 m telescope at Sierra Nevada Observatory and the 1.23 m telescope at Calar Alto observatory, allows us to derive possible three-dimensional shapes and density estimations for the body based on hydrostatic equilibrium assumptions. The effective diameter in equivalent area is around 84 km smaller than the radiometrically derived diameter using thermal data from
Herschel
and
Spitzer
Space Telescopes. This might indicate the existence of an unresolved satellite of up to ~300 km in diameter, which is required to account for all the thermal flux, although the occultation and thermal diameters are compatible within their error bars given the considerable uncertainty of the thermal results. The existence of a potential satellite also appears to be consistent with other ground-based data presented here. From the effective occultation diameter combined with absolute magnitude measurements we derive a geometric albedo of 0.147 ± 0.005, which would be somewhat smaller if 2002 TC
302
has a satellite. The best occultation light curves do not show any signs of ring features or any signatures of a global atmosphere.
From two observing runs during the 2014 summer at the Calar Alto Observatory in Almer...a (Spain) and at the Sierra Nevada Observatory in Granada (Spain), we were able to derive CCD photometry of the ...Trans-Neptunian object 2008 OG19. We analysed the time series and obtained a double-peaked light curve with a peak-to-valley amplitude of 0.437 plus or minus 0.011 mag and a rotational period of 8.727 plus or minus 0.003 h. This implies that this object is very elongated, closely resembling the case of Varuna. The photometry also allowed us to obtain an absolute magnitude in the R band of 4.39 plus or minus 0.07 mag. From this result, we estimated an equivalent diameter of 2008 OG19 of 619... km using an average albedo for scattered disc objects. Finally, we interpreted the results under the assumption of hydrostatic equilibrium and found a lower limit for the density of 544... kg m super( -3). However, a more likely density is 609 plus or minus 4 kg m super( -3) using an aspect angle of 60..., which corresponds to the most likely configuration for the spin axis with respect to the observer assuming random orientations. (ProQuest: ... denotes formulae/symbols omitted.)
Abstract
We present results from three world-wide campaigns that resulted in the detections of two single-chord and one multi-chord stellar occultations by the plutino object (84922) 2003 VS
2
. From ...the single-chord occultations in 2013 and 2014 we obtained accurate astrometric positions for the object, while from the multi-chord occultation on 2014 November 7, we obtained the parameters of the best-fitting ellipse to the limb of the body at the time of occultation. We also obtained short-term photometry data for the body in order to derive its rotational phase during the occultation. The rotational light curve present a peak-to-peak amplitude of 0.141 ± 0.009 mag. This allows us to reconstruct the 3D shape of the body, with principal semi-axes of
a
= 313.8 ± 7.1 km,
km, and
km, which is not consistent with a Jacobi triaxial equilibrium figure. The derived spherical volume equivalent diameter of
km is about 5% larger than the radiometric diameter of 2003 VS
2
derived from
Herschel
data of 523 ± 35 km, but still compatible with it within error bars. From those results we can also derive the geometric albedo (
) and, under the assumption that the object is a Maclaurin spheroid, the density
for the plutino. The disappearances and reappearances of the star during the occultations do not show any compelling evidence for a global atmosphere considering a pressure upper limit of about 1 microbar for a pure nitrogen atmosphere, nor secondary features (e.g., rings or satellite) around the main body.
Abstract
Background
Patients with colon Inflammatory Bowel Disease (IBD) have a higher risk of colorectal cancer (CRC) than general population. Current guidelines establish endoscopic surveillance ...recommendations; however, epidemiological studies show poor compliance. The main aim of our study was to analyse adherence to endoscopic surveillance guidelines. Secondary aim was to evaluate the prevalence and time-to advanced lesions or CRC.
Methods
Retrospective multicentre study of patients with IBD followed-up in the participating centres between 2005 and 2020, who were diagnosed of IBD between 2005 and 2008, with criteria for CRC surveillance. Patients with CRC before IBD diagnosis were excluded. The ECCO 2013–2017 guidelines were used to evaluate adherence. Adenomatous lesions with >25% of villous component, >1cm or with high-grade dysplasia or serrated lesions >1cm or with any degree of dysplasia were considered advanced lesions. Software used for all analysis was R in its 3.6.1 version. Normality was checked with the Shapiro-Wilks test. Mean comparison was carried out using t-Student test while normality assumptions held true, otherwise, Mann-Whitney test. Time-to advanced lesions or CRC event between patients that had adherence to ECCO guidelines versus those who did not was performed through Kaplan-Meier and Log-rank test. P-values below 0.05 were considered significant.
Results
A total of 1004 (713 Ulcerative Colitis, 252 Crohn’s disease and 39 Indeterminate Colitis; 52% male) patients from 25 centres were recruited with a median age of 36 (26–47) years. 87% of all patients were included in the endoscopic surveillance programme. The main reasons for non-inclusion were the absence of indication by the physician (38%) and the presence of inflammatory activity (37%). Adherence to the first or subsequent surveillance colonoscopies was 45% and 61%, respectively, with a total adherence rate of 32%. Prevalence of advanced lesions or CRC was 4% and 7 cases of CRC were detected. Time-to-detection of these lesions since IBD diagnosis was significantly longer in non-adherent patients (13.4 + 1.3 vs13.04 + 1.7; p<0.001). Adherence was associated to a higher detection of advanced lesions or CRC compared to non-adherent patients (HR: 1.97; IC: 1.02–3.79; p=0.043) (Figure 1).
Conclusion
Adherence to ECCO guidelines for endoscopic surveillance is low in this Southern European population. A higher and earlier detection of advanced lesions or CRC was identified in the adherent group. The results of this study highlight the need to improve compliance with the recommendations to obtain better outcomes.
Using data from the Infrared Array Camera on the Spitzer Space Telescope, we present photometric observations of a sample of 100 trans-Neptunian objects (TNOs) beyond 2.2 m. These observations, ...collected with two broadband filters centered at 3.6 and 4.5 m, were done in order to study the surface composition of TNOs, which are too faint to obtain spectroscopic measurements. With this aim, we have developed a method for the identification of different materials that are found on the surfaces of TNOs. In our sample, we detected objects with colors that are consistent with the presence of small amounts of water, and we were able to distinguish between surfaces that are predominantly composed of complex organics and amorphous silicates. We found that 86% of our sample have characteristics that are consistent with a certain amount of water ice, and the most common composition (73% of the objects) is a mixture of water ice, amorphous silicates, and complex organics. Twenty-three percent of our sample may include other ices, such as carbon monoxide, carbon dioxide, methane, or methanol. Additionally, only small objects seem to have surfaces dominated by silicates. This method is a unique tool for the identification of complex organics and to obtain the surface composition of extremely faint objects. Furthermore, this method will be beneficial when using the James Webb Space Telescope for differentiating groups within the trans-Neptunian population.
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