scholarly journals The large trans-Neptunian object 2002 TC302 from combined stellar occultation, photometry, and astrometry data

2020 ◽  
Vol 639 ◽  
pp. A134 ◽  
Author(s):  
J. L. Ortiz ◽  
P. Santos-Sanz ◽  
B. Sicardy ◽  
G. Benedetti-Rossi ◽  
R. Duffard ◽  
...  
Keyword(s):  
Physical Properties ◽  
Sierra Nevada ◽  
Thermal Flux ◽  
Absolute Magnitude ◽  
The Body ◽  
Light Curves ◽  
Effective Diameter ◽  
Near Misses ◽  
Considerable Uncertainty ◽  
Stellar Occultation

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 TC302. Methods. Stellar occultations offer unique opportunities to determine key physical properties of TNOs. On 28 January 2018, 2002 TC302 occulted a mv ~ 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 TC302 has a satellite. The best occultation light curves do not show any signs of ring features or any signatures of a global atmosphere.

scholarly journals The multi-chord stellar occultation by (19521) Chaos on 2020 November 20

2021 ◽  
Author(s):  
Mónica Vara-Lubiano ◽  
Nicolás Morales ◽  
Flavia Rommel ◽  
José Luis Ortiz ◽  
Bruno Sicardy ◽  
...  
Keyword(s):  
Solar System ◽  
Physical Properties ◽  
Sierra Nevada ◽  
Financial Support ◽  
European Space Agency ◽  
State Agency ◽  
Equivalent Diameter ◽  
Stellar Occultation ◽  
Stellar Occultations ◽  
Calar Alto

<p>Physical properties of Trans-Neptunian Objects (TNOs) have been of increasing interest in the last two decades, as these objects are considered to be among the least altered through the Solar System evolution, and thus preserve valuable information about its origin [1]. The study of these objects through the ground-based method of stellar occultations has risen in the last years, as this technique allows the determination of physical properties with considerably good accuracies [2,3,4]. </p> <p>Here we present the results of the multi-chord stellar occultation of the GAIA source 3444789965847631104 (m<sub>v</sub>≈16.8) by the TNO (19521) Chaos on 2020 November 20, which was predicted within our systematic programme on stellar occultations by TNOs and outer solar system bodies [5]. The prediction was updated with astrometric observations carried out two days before the event with the 1.23-m telescope at Calar Alto observatory in Almería, Spain, and it was favorable to the South of Europe. The campaign that we organized involved 19 observing sites and resulted in three positive detections, one of them obtained from the 4.2-m WHT telescope at La Palma, 11 negative detections, and 5 sites that could not observe due to bad weather.<em> </em></p> <p>We derived the instantaneous limb of Chaos by fitting the extremities of the positive chords to an ellipse to determine accurate size, shape, and geometric albedo for this object. The preliminary results give a slightly smaller area-equivalent diameter than the one derived from Herschel thermal data [6], but photometric observations of this object are still under analysis to complement and improve the results. <strong><br /><br /></strong><strong>References</strong></p> <p>[1] Morbidelli, A., Levison, H. F., & Gomes, R. 2008, ed. M. A. Barucci, H. Boehnhardt, D. P. Cruikshank, A. Morbidelli, R. Dotson, 275</p> <p>[2] Ortiz, J. L., Sicardy, B., Braga-Ribas, F., et al. 2012, Nature, 491, 566</p> <p>[3] Braga-Ribas, F., Sicardy, B., Ortiz, J. L., et al. 2013, ApJ, 773, 26</p> <p>[4] Ortiz, J.L., Santos-Sanz, P., Sicardy, B., et al. 2017, Nature, 550, 7675, pp. 219-223</p> <p>[5] Camargo, J. I. B., Vieira-Martins, R., Assafin, M., et al. 2014, A&A, 561, A37</p> <p>[6] Vilenius, E., Kiss, C., Mommert, M., Müller, T., et al. 2012, A&A, 541, A94 </p> <p><strong>Acknowledgements</strong><strong> </strong></p> <p>We acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). Part of the research leading to these results has received funding from the European Research Council under the European Community’s H2020 (2014-2020/ERC Grant Agreement no. 669416 “LUCKY STAR”). M.V-L. acknowledges funding from Spanish project AYA2017-89637-R (FEDER/MICINN). P.S-S. acknowledges financial support by the Spanish grant AYA-RTI2018-098657-J-I00 ``LEO-SBNAF'' (MCIU/AEI/FEDER, UE). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). We are grateful to the CAHA and OSN staffs. This research is partially based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by Junta de Andalucía and Consejo Superior de Investigaciones Científicas (IAA-CSIC). This research was also partially based on observation carried out at the Observatorio de Sierra Nevada (OSN) operated by Instituto de Astrofísica de Andalucía (CSIC). Partially based on observations made with the Tx40 telescope at the Observatorio Astrofísico de Javalambre in Teruel, a Spanish Infraestructura Cientifico-Técnica Singular (ICTS) owned, managed and operated by the Centro de Estudios de Física del Cosmos de Aragón (CEFCA). Tx40 is funded with the Fondos de Inversiones de Teruel (FITE).</p>

scholarly journals The stellar occultations by the largest satellite of the dwarf planet Haumea, Hi'iaka

2021 ◽  
Author(s):  
Estela Fernández-Valenzuela ◽  
Jose Luis Ortiz ◽  
Bryan Holler ◽  
Monica Vara-Lubiano ◽  
Nicolas Morales ◽  
...  
Keyword(s):  
Light Curve ◽  
North Africa ◽  
High Accuracy ◽  
The Body ◽  
Light Curves ◽  
Effective Diameter ◽  
Preliminary Results ◽  
Stellar Occultations ◽  
The Times ◽  
Triaxial Shape

<p>Two stellar occultations by the largest satellite of the dwarf planet Haumea, Hi'iaka, were predicted to happen on April, 6th and 16th, 2021. Additional high accuracy astrometric analysis was carried out in order to refine the prediction for April 6th, using several telescopes in the 1.2-m to 2-m range, with the final shadow path crossing North Africa. We successfully detected the first event from TRAPPIST-North telescope at Oukaïmeden Observatory (Morocco). Although it was recorded from only one site, this first detection allowed us to improve the prediction for the second that crossed North America from East to West. We had a good success recording six positive detections and several negative detections that constrain the shape and size of the body. The light curves obtained from the different observatories provide the time at which the star disappears and reappears, which are translated into chords (the projected lines on the sky-plane as observed from each location). Additionally, we carried out a campaign to study Hi'iaka's rotational light-curve, studying the residuals of Haumea's rotational light-curve to a four-order Fourier fit. We obtained the rotational phases at the times of the occultations, which is critical for the analysis of the occultations, given that Hi’iaka is clearly non-spherical. Our preliminary results show that Hi'iaka indeed has a triaxial shape with a larger effective diameter than what has been published so far. The preliminary results and their implications will be discussed in this talk. </p>

scholarly journals Physical model of near-Earth asteroid (1917) Cuyo from ground-based optical and thermal-IR observations

2019 ◽  
Vol 627 ◽  
pp. A172
Author(s):  
A. Rożek ◽  
S. C. Lowry ◽  
B. Rozitis ◽  
S. F. Green ◽  
C. Snodgrass ◽  
...  
Keyword(s):  
Light Curve ◽  
Physical Properties ◽  
Physical Model ◽  
Spin State ◽  
Physical Modelling ◽  
Light Curves ◽  
Compositional Variation ◽  
Effective Diameter ◽  
Surface Material ◽  
Earth Asteroid

Context. The near-Earth asteroid (1917) Cuyo was subject to radar and light curve observations during a close approach in 1989, and observed up until 2008. It was selected as one of our ESO Large Programme targets, aimed at observational detections of the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect through long-term light curve monitoring and physical modelling of near-Earth asteroids. Aims. We aim to constrain the physical properties of Cuyo: shape, spin-state, and spectroscopic and thermo-physical properties of the surface. Methods. We acquired photometric light curves of Cuyo spanning the period between 2010 and 2013, which we combined with published light curves from 1989 to 2008. Our thermal-infrared observations were obtained in 2011. Rotationally resolved optical spectroscopy data were acquired in 2011 and combined with all available published spectra to investigate any surface material variegation. Results. We developed a convex light curve-inversion shape of Cuyo that suggests the presence of an equatorial ridge, typical for an evolved system close to shedding mass due to fast rotation. We determine limits of YORP strength through light curve-based spin-state modelling, including both negative and positive acceleration values, between − 0.7 × 10−8 and 1.7 × 10−8 rad day−2. Thermo-physical modelling with the ATPM provides constraints on the geometric albedo, pV = 0.24 ± 0.07, the effective diameter, Deff = 3.15 ± 0.08 km, the thermal inertia, Γ = 44 ± 9 J m−2 s−1∕2 K−1, and a roughness fraction of 0.52  ±  0.26. This enabled a YORP strength prediction of ν = (−6.39 ± 0.96) × 10−10 rad day−2. We also see evidence of surface compositional variation. Conclusions. The low value of YORP predicted by means of thermo-physical analysis, consistent with the results of the light curve study, might be due to the self-limiting properties of rotational YORP, possibly involving movement of sub-surface and surface material. This may also be consistent with the surface compositional variation that we see. The physical model of Cuyo can be used to investigate cohesive forces as a way to explain why some targets survive rotation rates faster than the fission limit.

scholarly journals A multi-chord stellar occultation by the large trans-Neptunian object (174567) Varda

2020 ◽  
Vol 643 ◽  
pp. A125 ◽  
Author(s):  
D. Souami ◽  
F. Braga-Ribas ◽  
B. Sicardy ◽  
B. Morgado ◽  
J. L. Ortiz ◽  
...  
Keyword(s):  
Absolute Magnitude ◽  
The Body ◽  
The Other ◽  
Main Body ◽  
Equivalent Radius ◽  
Stellar Occultation ◽  
The Usa ◽  
Best Fitting ◽  
Low Amplitude ◽  
Geometric Albedo

Context. We present results from the first recorded stellar occultation by the large trans-Neptunian object (174567) Varda that was observed on September 10, 2018. Varda belongs to the high-inclination dynamically excited population, and has a satellite, Ilmarë, which is half the size of Varda. Aims. We determine the size and albedo of Varda and constrain its 3D shape and density. Methods. 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 Varda’s mass as is known from previous works. Results. The best-fitting elliptical limb has semi-major (equatorial) axis of (383 ± 3) km and an apparent oblateness of 0.066 ± 0.047, corresponding to an apparent area-equivalent radius R′equiv = (370±7) km and geometric albedo pv = 0.099 ± 0.002 assuming a visual absolute magnitude HV = 3.81 ± 0.01. Using three possible rotational periods for the body (4.76, 5.91, and 7.87 h), we derive corresponding MacLaurin solutions. Furthermore, given the low-amplitude (0.06 ± 0.01) mag of the single-peaked rotational light-curve for the aforementioned periods, we consider the double periods. For the 5.91 h period (the most probable) and its double (11.82 h), we find bulk densities and true oblateness of ρ = (1.78 ± 0.06) g cm−3, ɛ = 0.235 ± 0.050, and ρ = (1.23 ± 0.04) g cm−3, ɛ = 0.080 ± 0.049. However, it must be noted that the other solutions cannot be excluded just yet.

An investigation of Pluto’s troposphere using stellar occultation light curves and an atmospheric radiative–conductive–convective model

Icarus ◽  
2011 ◽  
Vol 214 (2) ◽  
pp. 685-700 ◽  
Author(s):  
Angela M. Zalucha ◽  
Xun Zhu ◽  
Amanda A.S. Gulbis ◽  
Darrell F. Strobel ◽  
J.L. Elliot
Keyword(s):  
Light Curves ◽  
Stellar Occultation ◽  
Convective Model

scholarly journals Understanding Type II Supernovae

2005 ◽  
Vol 192 ◽  
pp. 275-280 ◽  
Author(s):  
L. Zampieri ◽  
M. Ramina ◽  
A. Pastorello
Keyword(s):  
Physical Properties ◽  
Large Range ◽  
Simultaneous Analysis ◽  
Light Curves ◽  
Physical Parameters ◽  
Expansion Velocity ◽  
Type Ii ◽  
Strong Correlations ◽  
Systematic Analysis ◽  
Robust Estimates

SummaryWe present the results of a systematic analysis of a group of Type II plateau supernovae that span a large range in luminosities, from faint objects like SN 1997D and 1999br to very luminous events like SN 1992am. The physical properties of the supernovae appear to be related to the plateau luminosity or the expansion velocity. The simultaneous analysis of the observed light curves, line velocities and continuum temperatures leads us to robust estimates of the physical parameters of the ejected envelope. We find strong correlations among several parameters. The implications of these results regarding the nature of the progenitor, the central remnant and the Ni yield are also addressed.

Platelet Mechanosensing: Adhesion and Spreading On Immobilized Fibrinogen Depends On Substrate Stiffness

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 384-384
Author(s):  
Yongzhi Qiu ◽  
Ashley C Brown ◽  
Woo Jin Jung ◽  
Yumiko Sakurai ◽  
Robert Mannino ◽  
...  
Keyword(s):  
Physical Properties ◽  
Platelet Adhesion ◽  
The Body ◽  
Substrate Stiffness ◽  
Fibrinogen Concentration ◽  
Spreading Area ◽  
Significant Difference ◽  
The Difference ◽  
Underlying Substrate ◽  
Covalently Bound

Abstract Abstract 384 Background: Whereas surface-immobilized fibrinogen readily causes platelet adhesion and spreading, soluble fibrinogen, on the other hand, does not lead to platelet activation without the presence of other hemostatic/thrombotic signals. This dramatically different response of platelets to fibrinogen may be due to biochemical difference in fibrinogen unfolding (Agnihotri, et al., Langmuir, 2004), but may also be due to the difference in how platelets directly react to the physical properties of the substrate underneath the fibrinogen. Similarly, recent studies have shown that many types of adherent eukaryotic cells respond differently to substrates of different physical properties. In particular, cells are able to mechanosense the stiffness of their underlying substrate, and to change their spreading, re-organize their cytoskeleton, and even alter gene expression responding to the sensed stiffness (Discher, et al., Science, 2005). More specific to platelets, our group has recently shown that the contraction of single platelets on fibrinogen surfaces increases with increasing substrate stiffness (Lam, et al., Nat Mater, 2011). Therefore, we hypothesize that substrate stiffness can also affect platelet adhesion and spreading on fibrinogen. In this study, we synthesized polyacrylamide (PAA) gels, which can be tuned to different stiffnesses and easily modified with covalently-bound fibrinogen on the surface. This assay enables independent control of substrate stiffness while maintaining constant biochemical composition and fibrinogen density, and we applied this system to quantitatively investigate the role of substrate stiffness in platelet adhesion and spreading on fibrinogen. Results and Discussions: 3 μg/ml fibrinogen was covalently bound to the surface of PAA gels of different stiffnesses (0.25, 0.5, 2.5, 5, 50 and 100 kilopascals (KPa)) (Figure 1A). This applied range of substrate stiffness mimics the stiffness of different tissues in the body (Engler, et al., Cell, 2006). Moreover, glass (with a stiffness of ∼65–70 × 103 KPa) adsorbed with 3 μg/ml fibrinogen was also used for comparison. During 2 hour incubations, washed human platelets differently adhered to and spread on the surface of PAA gels. By simply varying the stiffness of the fibrinogen-bound PAA gels, we observed dramatic differences in the number of adherent platelets and their morphology (Figure 1B). The number of adherent platelets increased with increasing stiffness, reaching a plateau at 2.5 KPa, with adherence similar to that of fibrinogen-adsorbed glass (Figure 1C). While platelets did not spread on 2.5 KPa and softer gels, approximately 30–40% adherent platelets spread on 5KPa and stiffer gels, resulting in a significantly higher average spreading area of adherent platelets (Figure 1D and E). However, compared to all the gels, mostly all platelets adhered on glass surface spread (area > 35 μm2) and showed a significantly higher spreading area (Figure 1D and E). Moreover, no significant difference in fibrinogen concentration was detected among fibrinogen-bound PAA gels of different stiffnesses and fibrinogen-adsorbed glass (Data not shown), which indicated that the difference we observed could be independently due to the substrate stiffness. Conclusions and Ongoing Efforts: Our data suggest that platelets sense the mechanical properties of the underlying substrate to fine-tune the degree of adhesion and spreading on fibrinogen. Thus, fibrinogen on soft substrates appears to activate platelets to a lesser degree than the same concentration of fibrinogen on stiffer substrates. We are currently investigating how substrate stiffness triggers mechanotransduction in platelets and affects their outside-in activation and signaling. Our study also provides potential insights for preventing clot formation on implanted biomaterials and medical devices. Disclosures: No relevant conflicts of interest to declare.

Maternal influence on juvenile growth rates in Belding's ground squirrel (Spermophilus beldingi)

1991 ◽  
Vol 69 (8) ◽  
pp. 2140-2145 ◽  
Author(s):  
Stephen C. Trombulak
Keyword(s):  
Body Mass ◽  
Sierra Nevada ◽  
Early Summer ◽  
Ground Squirrels ◽  
The Body ◽  
Supplemental Food ◽  
Sierra Nevada Mountains ◽  
Extra Food ◽  
Spermophilus Beldingi ◽  
Reproductive Females

The influence of food acquisition by pregnant and lactating Belding's ground squirrels (Spermophilus beldingi) on the body mass and growth rate of their offspring was assessed in a free-ranging population. In late spring and early summer of 1985 and 1986, individual females in a population of Belding's ground squirrels in the Sierra Nevada Mountains of California were given 300–500 g of sunflower seeds daily at the entrances to their burrows. Juveniles born to mothers who received supplemental food emerged from natal burrows on average 28% heavier than did controls (73.0 vs. 57.1 g, P < 0.001) and maintained a greater body mass throughout the remainder of the summer (P < 0.01). Also, females had a nonsignificant tendency towards greater survivorship during their first winter (P = 0.09). Supplemental feeding had no effect on litter size or sex ratio of offspring, or on the mass of the mothers up to the time of weaning, indicating that extra food available in the spring to reproductive females is converted primarily, if not exclusively, into larger offspring. Because the lengths of gestation and lactation are relatively invariable, the greater body mass of emerging juveniles must result from faster growth prior to weaning.

Dynamics of tracheal compression in the horned passalus beetle

2013 ◽  
Vol 304 (8) ◽  
pp. R621-R627 ◽  
Author(s):  
James S. Waters ◽  
Wah-Keat Lee ◽  
Mark W. Westneat ◽  
John J. Socha
Keyword(s):  
Dynamical Behavior ◽  
The Body ◽  
Reverse Direction ◽  
Effective Diameter ◽  
Contrast Imaging ◽  
Tracheal System ◽  
Tracheal Compression ◽  
Internal Mixing ◽  
Respiratory Gases ◽  
Opening And Closing

Rhythmic patterns of compression and reinflation of the thin-walled hollow tubes of the insect tracheal system have been observed in a number of insects. These movements may be important for facilitating the transport and exchange of respiratory gases, but observing and characterizing the dynamics of internal physiological systems within live insects can be challenging due to their size and exoskeleton. Using synchrotron X-ray phase-contrast imaging, we observed dynamical behavior in the tracheal system of the beetle, Odontotaenius disjunctus. Similar to observations of tracheal compression in other insects, specific regions of tracheae in the thorax of O. disjunctus exhibit rhythmic collapse and reinflation. During tracheal compression, the opposing sides of a tracheal tube converge, causing the effective diameter of the tube to decrease. However, a unique characteristic of tracheal compression in this species is that certain tracheae collapse and reinflate with a wavelike motion. In the dorsal cephalic tracheae, compression begins anteriorly and continues until the tube is uniformly flattened; reinflation takes place in the reverse direction, starting with the posterior end of the tube and continuing until the tube is fully reinflated. We report the detailed kinematics of this pattern as well as additional observations that show tracheal compression coordinated with spiracle opening and closing. These findings suggest that tracheal compression may function to drive flow within the body, facilitating internal mixing of respiratory gases and ventilation of distal regions of the tracheal system.

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