Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe 2017 May 20$^{rm th}$ stellar occultation by the elongated centaur (95626) 2002 GZ$_{32}$
464
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We predicted a stellar occultation of the bright star Gaia DR1 4332852996360346368 (UCAC4 385-75921) (m$_{rm V}$= 14.0 mag) by the centaur 2002 GZ$_{32}$ for 2017 May 20$^{rm th}$. 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 multi-chord stellar occultation is reported. By means of an elliptical fit to the occultation chords we obtained the limb of 2002 GZ$_{32}$ during the occultation, resulting in an ellipse with axes of 305 $pm$ 17 km $times$ 146 $pm$ 8 km. From this limb, thanks to a rotational light curve obtained shortly after the occultation, we derived the geometric albedo of 2002 GZ$_{32}$ ($p_{rm V}$ = 0.043 $pm$ 0.007) and a 3-D ellipsoidal shape with axes 366 km $times$ 306 km $times$ 120 km. This shape is not fully consistent with a homogeneous body in hydrostatic equilibrium for the known rotation period of 2002 GZ$_{32}$. 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 GZ$_{32}$ were detected from the occultation, but narrow and thin rings cannot be discarded.
rate research
Read More
On 28th January 2018, the large Trans-Neptunian Object (TNO) 2002TC302 occulted a m$_v= $15.3 star with ID 130957813463146112 in the Gaia DR2 stellar catalog. 12 positive occultation chords were obtained from Italy, France, Slovenia and Switzerland. Also, 4 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, compatible with the near misses, can be obtained. The resulting ellipse has major and minor axes of 543 $pm$ 18 km and 460 $pm$ 11 km, respectively, with a position angle of 3 $pm$ 1 degrees for the minor axis. This information, combined with rotational light curves obtained with the 1.5m telescope at Sierra Nevada Observatory and the 1.23m telescope at Calar Alto observatory, allows us to derive possible 3D shapes and density estimations for the body, based on hydrostatic equilibrium assumptions. The effective area equivalent diameter is $sim$ 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 $sim$ 300 km in diameter, 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 H$_V$ measurements we derive a geometric albedo of 0.147 $pm$ 0.005, which would be somewhat smaller if 2002TC302 has a satellite. The best occultation light curves do not show any signs of ring features or any signatures of a global atmosphere.
The Fermi-Large Area Telescope (LAT) detection of the X8.2 GOES class solar flare of 2017 September 10 provides for the first time observations of a long duration high-energy gamma-ray flare associated with a Ground Level Enhancement (GLE). The >100 MeV emission from this flare lasted for more than 12 hours covering both the impulsive and extended phase. We present the localization of the gamma-ray emission and find that it is consistent with the active region (AR) from which the flare occurred over a period lasting more than 6 hours contrary to what was found for the 2012 March 7 flares. The temporal variation of the proton index inferred from the gamma-ray data seems to suggest two phases in acceleration of the proton population. Based on timing arguments we interpret the second phase to be tied to the acceleration mechanism powering the GLE, believed to be particle acceleration at a coronal shock driven by the CME.
We present results from the first recorded stellar occultation by the large trans-Neptunian object (174567) Varda that was observed on September 10$^{rm th}$, 2018. Varda belongs to the high-inclination dynamically excited population, and has a satellite, Ilmare, which is half the size of Varda. We determine the size and albedo of Varda and constrain its 3D shape and density. Thirteen different sites in the USA monitored the event, five of which detected an occultation by the main body. A best-fitting ellipse to the occultation chords provides the instantaneous limb of the body, from which the geometric albedo is computed. The size and shape of Varda are evaluated, and its bulk density is constrained, using Vardas mass known from previous works. The best-fitting elliptical limb has semi-major (equatorial) axis of $(383 pm 3)$km and an apparent oblateness $0.066pm0.047$ corresponding to an apparent area-equivalent radius $R_{rm equiv}= (370pm7)$km and geometric albedo $p_v=0.099pm 0.002 $ assuming a visual absolute magnitude $H_V=3.81pm0.01$. Using three possible rotational periods for the body (4.76h, 5.91h, and 7.87h), we derive corresponding MacLaurin solutions. Furthermore, given the low-amplitude ($0.06pm0.01$) mag of the single-peaked rotational light-curve for the aforementioned periods, we consider the double periods. For the 5.91h period (the most probable) and its double (11.82h), we find bulk densities and true oblateness of $rho=(1.78pm0.06)$ g cm$^{-3}$, $epsilon=0.235pm0.050$ and $rho=(1.23pm0.04)$ g cm$^{-3}$, $epsilon=0.080pm0.049$. However, it must be noted that the other solutions cannot be excluded just yet.
Plutos atmospheric profiles (temperature and pressure) have been studied for decades from stellar occultation lightcurves. In this paper, we look at recent Pluto Global Climate Model (GCM) results (3D temperature, pressure, and density fields) from Bertrand et al. (2020) and use the results to generate model observers plane intensity fields (OPIF) and lightcurves by using a Fourier optics scheme to model light passing through Plutos atmosphere (Young, 2012). This approach can accommodate arbitrary atmospheric structures and 3D distributions of haze. We compared the GCM model lightcurves with the lightcurves observed during the 15-AUG-2018 Pluto stellar occultation. We find that the climate scenario which best reproduces the observed data includes an N2 ice mid-latitude band in the southern hemisphere. We have also studied different haze and P/T ratio profiles: the haze effectively reduces the central flash strength, and a lower P/T ratio both reduces the central flash strength and incurs anomalies in the shoulders of the central flash.
We observed the July 17, 2017 stellar occultation of HD 168233 by the Kuiper Belt Object (486958) 2014 MU$_{69}$, the close flyby target of the extended New Horizons mission. Rather than capture a solid body occultation by the KBO itself, our program aimed to constrain the opacity of rings, moons, or other debris in the nearby environment. We used the Hubble Space Telescope Fine Guidance Sensors (HST FGS) instrument in TRANS F583W mode to collect 40 Hz time resolution photometry of the stellar occultation star for two HST orbits during this observation. We present the results of reduction and calibration of the HST FGS photometry, and set upper limits on rings or other dust opacity within the Hill sphere of (486958) 2014 MU$_{69}$ at distances ranging from $sim$20,000 km to $sim$75,000 km from the main body.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
