Papers by Pablo Santos Sanz
<p align="justify"><strong>Abstract</strong></p> <p lang=&qu... more <p align="justify"><strong>Abstract</strong></p> <p lang="en-US" align="justify">Centaurs and trans-Neptunian objects (TNOs) are considered to be the most pristine members of our solar system, beside Oort cloud objects.</p> <p lang="en-US" align="justify">The observation of stellar occultations by solar system objects is a powerful technique to directly measure their size and profile shapes with kilometer accuracy [e.g. 1, and references therein], to probe the environment of them with the possibility to reveal satellites and / or rings [e.g. 2, 3] and to detect or to constrain an atmosphere down to the nanobar level [e.g. 4]. Finally it provides a high-accuracy astrometric measurement, which can for example be used for improving the prediction of subsequent occultation events within short or mid-term time spans.</p> <p lang="en-US" align="justify"><span lang="en-GB">Here we report the observation of an occultation event of the star Gaia DR2 4111560308371475840 (G = 14.6 mag) by the TNO (119951) 2002 KX</span><sub><span lang="en-GB">14</span></sub><span lang="en-GB"> on May 26, 2020. The shadow was predicted to cross eastern Europe (Fig. 1) and the event was observed successfully by </span><span lang="en-US">ten</span><span lang="en-GB"> stations supplemented by another good dozen of stations which had a miss (no event detected).</span></p> <p lang="en-US" align="justify"><span lang="en-GB">2002 KX</span><sub><span lang="en-GB">14</span></sub><span lang="en-GB"> is a low-inclination (</span><span lang="en-GB"><em>i</em></span><span lang="en-GB"> ~ 0.4&#176;), low-eccentricity (</span><span lang="en-GB"><em>e</em></span><span lang="en-GB"> ~ 0.04) cold classical TNO, orbiting the Sun at an average distance of </span><span lang="en-GB"><em>a</em></span><span lang="en-GB"> ~ 39 au. The radiometric diameter is given as 455 </span><span lang="en-GB">&#177; 27 km [</span><span lang="en-GB">5</span><span lang="en-GB">]. </span><span lang="en-GB">On April 26, 2012, an occultation by this object was observed with the 4.2-m William Herschel Telescope on La Palma (Spain) at high cadence. From this single-chord observation (with a chord length of 415 </span><span lang="en-GB">&#177; </span><span lang="en-GB">1 km), combined with accurate astrometry at the time of occultation, an area-equivalent diameter of at least 365 (</span><span lang="en-GB">+30, -21)</span><span lang="en-GB"> km was estimated [6]. The rotational period is yet unknown. The lightcurve amplitude is reported as </span><span lang="en-GB">&#916;</span><span lang="en-GB"><em>m&#160;</em></span><span lang="en-GB"><&#160;0.05&#160;mag (from 3 nights, [7</span><span lang="en-US">]</span><span lang="en-GB">). </span></p> <p lang="en-US" align="justify">The occultation was predicted within the Lucky Star project. 121 astrometric observations filed at the MPC plus 56 observations derived at observatories used by the LS collaboration, covering the time span 1984-2018, were used to derive the NIMAv7 [8] orbit solution, which was used for the occultation event search. As the event was suitable to be observed by smaller telescopes, the amateur community was informed via mail lists etc. Details of the prediction are given on the LS project website [9].</p> <p lang="en-US" align="justify"><span lang="en-GB">Ten stations recorded the occultation with apertures between 20 cm and 80 cm. Five of them used analogue video technique for the recording, and five&#160; applied CCD cameras. 14 stations reported a non-detection of </span><span lang="en-GB">the</span><span lang="en-GB"> occultation event within their observing windows (Fig. 1)</span><span lang="en-GB">.</span></p> <p lang="en-US" align="justify"><span lang="en-GB">By </span><span lang="en-GB">applying the method described in [10], w</span><span lang="en-GB">e fitted the extremities of the positive chords to an ellipse to derive the instantaneous limb of 2002 KX</span><sub><span lang="en-GB">14</span></sub><span lang="en-GB">. From the five fit parameters (center of the ellipse, semi-major and semi-minor axis and the position angle of the semi-minor axis) we derived the size and shape of the 2D limb as well as a high-accurate astrometric position for the time of occultation. </span><span lang="en-GB">Photometric observations to derive the light curve amplitude and the rotational period, with the aim to put constraints on the albedo as well as on the 3D size and the shape of 2002 KX</span><sub><span lang="en-GB">14</span></sub><span lang="en-GB"> are planned.</span></p> <p lang="en-US" align="justify"><strong>Acknowledgements</strong></p> <p lang="en-US" align="left"><span lang="en-US">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 Astrof&#237;sica de Andaluc&#237;a (SEV-2017-0709) and the financial support by the Spanish grant AYA-2017-84637-R. M.V-L. acknowledges funding from Spanish project…
ABSTRACT We observed a sample of 18 Centaurs with the PACS instrument on-board Herschel Space Obs... more ABSTRACT We observed a sample of 18 Centaurs with the PACS instrument on-board Herschel Space Observatory. The observations cover the wavelength range where the thermal emission from trans-Neptunian objects has its maximum. After reduction, background cleaning, and flux extraction we determined the sizes and albedos for all the members of the sample using thermophysical models. In this work we will present new results on sizes and albedos and possible correlations with physical and dynamical parameters like colors, spectral slopes, semimajor axis, eccentricities, orbital inclinations, etc.
&lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;Eris is cu... more &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;Eris is currently the most massive known dwarf planet in the Solar system, it has one known satellite, Dysnomia (Brown &amp; Schaller 2007; Holler et al. 2020). There have been several attempts trying to identify the rotation period of Eris from visible ground based measurements which resulted in a wide range of possible values (Duffard et al., 2008). Here we present some new light curve data of Eris, taken with &amp;#8764;1m-class ground based telescopes, with the GROND instrument at the 2.2m MPG/ESO telescope La Silla, and also with the Transiting Exoplanet Survey Satellite (TESS).&lt;/span&gt;&lt;/p&gt; &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;&lt;img src="" alt="" width="1067" height="259" /&gt;&lt;/span&gt;&lt;/p&gt; &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;Observations of Eris with GROND were made in 3 nights in August 2010. Auxiliary ground based photometry data of Eris from five telescopes were obtained in irregular intervals between 2005 and 2020 (see table 1.) TESS observed Eris in Sector 30 with its Camera 1 and CCD 3. A significant portion of the light curve data had to be excluded due to Eris&amp;#8217; encounter with nearby background sources which left a dominant feature in the background-subtracted image. We note that due to the limited length of the TESS light blocks (2.3 d and 6.6 d) it was not possible to detect light curve periods in to order or close to the orbital period (15.78 d).&lt;/span&gt;&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;&lt;img src="" alt="" width="1035" height="414" /&gt;&lt;/p&gt; &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt; &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;For most of the ground-based measurements we used our night-averaged values for the 1.5m, La Hita and CA2.2m data), except for the GROND measurements, for which we used the all the individual data points. In addition, we also considered previously published data, including ground-based data from Carraro et al., 2006 and Duffard et al., 2008, and the SWIFT satellite data from Roe et al., 2008.&lt;br /&gt;&lt;/span&gt;&lt;/p&gt; &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;We assumed that i) the light curve amplitude is the same in any of the photometric bands used and ii) the light curve can be described by a simple sinusoidal variation. With these assumptions each model light curve can be described by four parameters: a light curve amplitude, period, phase-shift, and an offset from the photometric zero point. We allowed a different offset for each measurement block even if the data were taken by the same instrument and filter combination (1.5m measurements) due to the year-long gaps between the measurement blocks. We chose an amplitude A and period P, and determined the best fitting light curve phase using a Levenberg&amp;#8211;Marquardt minimization algorithm. We expect that the best-fitting period-amplitude values provide the lowest C(P,A) values. We searched the period range P &amp;#8712; [1d, 15.88 d], where 15.88 d is the orbital period of Dysnomia, and it would correspond to a synchronised rotation. The C(P,A) contour map shows two minima, one at P &amp;#8776; 8 h, and A &amp;#8776; 0.05, and another at P &amp;#8776; 11.5 h, and A &amp;#8776; 0.08. To check the robustness of this result, we repeated the process by modifying the photometric data points by adding a random value with normal distribution and repeating the fitting process several times for the whole data set. The same two minima popped up in all cases. TESS data favours a rotation period of 59.420&amp;#177;0.527 h (See Figure 1.), while ground based data is more compatible with a synchronous or nearly synchronous rotation (See Figure 2.).&lt;/span&gt;&lt;/p&gt; &lt;p&gt;&lt;img src="" alt="" width="1027" height="570" /&gt;&lt;/p&gt; &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;We inspected the colours calculated from the GROND photometry and compared our results to previous values from the literature (Table 2). The optical colours (B-V, V-R, R-I) are in good agreement with previous colours, but the J-H colour from GROND is different from the ones in the literature. Also, we can see a big scatter in those. (See Table 2.)&lt;br /&gt;&lt;/span&gt;&lt;/p&gt; &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt;&lt;img src="" alt="" width="1070" height="498" /&gt;&lt;br /&gt;&lt;/span&gt;&lt;/p&gt; &lt;p&gt;&lt;span dir="ltr" role="presentation"&gt; One possible explanation can be, that there is a big CH4 feature on the surface of Eris, which has strong absorption lines&amp;#160; in H band, and it can change the NIR colour, but not the optical ones. To confirm this, more long-term optical and NIR measurements are needed. Finally, we use the simple tidal evolution code by Hastings et al. (2016) to calculate the evolution of the satellite orbit (only the semi-major axis in this approximation) and the spin…
Astronomy & Astrophysics
Context. Stellar occultation is a powerful technique that allows the determination of some physic... more Context. Stellar occultation is a powerful technique that allows the determination of some physical parameters of the occulting object. The result depends on the photometric accuracy, the temporal resolution, and the number of chords obtained. Space telescopes can achieve high photometric accuracy as they are not affected by atmospheric scintillation. Aims. Using ESA’s CHEOPS space telescope, we observed a stellar occultation by the transneptunian object (50000) Quaoar. We compare the obtained chord with previous occultations by this object and determine its astrometry with sub-milliarcsecond precision. Also, we determine upper limits to the presence of a global methane atmosphere on the occulting body. Methods. We predicted and observed a stellar occultation by Quaoar using the CHEOPS space telescope. We measured the occultation light curve from this dataset and determined the dis- and reappearance of the star behind the occulting body. Furthermore, a ground-based telescope in Aust...
arXiv: Earth and Planetary Astrophysics, 2009
We analyze a vast light curve database by obtaining mean rotational properties of the entire samp... more We analyze a vast light curve database by obtaining mean rotational properties of the entire sample, determining the spin frequency distribution and comparing those data with a simple model based on hydrostatic equilibrium. For the rotation periods, the mean value obtained is 6.95 h for the whole sample, 6.88 h for the Trans-neptunian objects (TNOs) alone and 6.75 h for the Centaurs. From Maxwellian fits to the rotational frequencies distribution the mean rotation rates are 7.35 h for the entire sample, 7.71 h for the TNOs alone and 8.95 h for the Centaurs. These results are obtained by taking into account the criteria of considering a single-peak light curve for objects with amplitudes lower than 0.15 mag and a double-peak light curve for objects with variability >0.15mag. The best Maxwellian fits were obtained with the threshold between 0.10 and 0.15mag. The mean light-curve amplitude for the entire sample is 0.26 mag, 0.25mag for TNOs only, and 0.26mag for the Centaurs. The am...
Even though there are more than 1300 Transneptunian Objects discovered so far, less than 5% of th... more Even though there are more than 1300 Transneptunian Objects discovered so far, less than 5% of them have a well determined rotational period. We compile the results of 6 years of observations from our Kuiper Belt lightcurve survey in Spain. Our main aim was to increase the number of objects whose short-term variability has been studied in order to be
Se permite la reproducción de cualquier texto o imagen contenidos en este ejemplar citando como f... more Se permite la reproducción de cualquier texto o imagen contenidos en este ejemplar citando como fuente "IAA: Información y Actualidad Astronómica" y al autor o autores.
Uploads
Papers by Pablo Santos Sanz