Long-term photometric analysis of the trans-Neptunian object 2008 OG19
Authors: Costa-Sitjà Marc , Fernández-Valenzuela Estela , Ortiz José Luis , Morales Nicolás , Santos-Sanz Pablo , Vara-Lubiano Mónica 
Published: September 2022

&lt;p&gt;We have carried out a long term photometric analysis of time series images of the trans-Neptunian object (TNO) 2008 OG&lt;sub&gt;19&lt;/sub&gt; with which we have refined its physical properties from its long-term variability.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Photometric Analysis&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;The first detailed analysis of 2008 OG&lt;sub&gt;19&lt;/sub&gt; was carried out by [1] using rotational light-curves from 2014 and 2016 from which a volume-equivalent diameter, a rotation period (P), a triaxial ellispoidal shape model, and a density were estimated.&lt;/p&gt;
&lt;p&gt;We have used 1,314 images covering a time-span of six years (2014-2021), obtained with the Sierra Nevada 1.5-m telescope and the Calar Alto 1.2-m telescope, both in Spain, in order to build yearly rotational light-curves for 2008 OG&lt;sub&gt;19&lt;/sub&gt;. To refine the rotation period estimation of 2008 OG&lt;sub&gt;19&lt;/sub&gt;, we have combined the whole set of data and applyed the lomb periodogram [2] and the Phase Dispersion Minimization techniques [3] resulting in P = 8.72565 +/- 0.0008 hr. The resulting rotational light-curve can be seen in Figure 1.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;Long-term variability&lt;/strong&gt;&lt;/p&gt;
&lt;p&gt;By folding the light-curves with the refined period, we have been able to see an increase of the amplitude of the rotational light-curve. This increase is due to a change in the aspect angle, that allows to estimate the orientation of 2008 OG&lt;sub&gt;19&lt;/sub&gt; rotational axis as seen in Figure 2. Using the largest rotational light-curve amplitude and assuming hydrostatic equilibrium we have updated its triaxial ellispoid model and its density.&lt;/p&gt;
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&lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;493&quot; height=&quot;339&quot; /&gt;&lt;/p&gt;
&lt;p&gt;Figure 1: 2008 OG&lt;sub&gt;19&lt;/sub&gt; rotational light-curves folded to P = 8.72565 h. Observational data are represented by color points with each color indicating a different observational night. The black dashed line represent the Fourier series fit.&lt;/p&gt;
&lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;537&quot; height=&quot;402&quot; /&gt;&lt;/p&gt;
&lt;p&gt;Figure 2: Model of the amplitude given by the fit to the observational data using b/a = 0.643 in blue (best fit). Other pole solutions are possible with different values of the b/a such as the red model. The gray line represents 2008 OG&lt;sub&gt;19&lt;/sub&gt; aspect angle given by the best fit. The magenta points with error bars are the observational data from this work.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;[1] E. d. M. Fern&amp;#225;&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;ndez-Valenzuela, &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Physical properties of transneptunian objects and centaurs; Ph.D. &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;thesis, University of Granada, Spain, 2017.&lt;/span&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;[2] N. R. Lomb,&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Least-squares frequency analysis of unequally spaced &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;data, Astrophysics and Space Science 39 (1976) 447&amp;#8211;462. doi:&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;10.1007/&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;BF00648343&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;.&lt;/span&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;[3] R. F. Stellingwerf,&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Period determination using phase dispersion mini&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;mization, ApJ 224 (1978) 953&amp;#8211;960. doi:&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;10.1086/156444&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;.&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;2&lt;/span&gt;&lt;/p&gt;
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