Herschel/SPIRE photometry of targeted and serendipitously observed asteroids
Authors: Szakáts Róbert , Kiss Csaba , Müller Thomas , Valtchanov Ivan 
Published: September 2022

&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;The Herschel Space Observatory observed with its PACS and SPIRE instruments a diverse selection of astronomical objects, &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;including Solar System objects (SSOs), either in dedicated measurements or serendipitously.&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;The infrared observations of&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;asteroids helped scientists to determine their physical and thermal properties. In addition, PACS and SPIRE observations&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;of selected large asteroids were used for a wide range of calibration aspects. Due to their strong thermal emission, SSOs may &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;sporadically also contaminate the photometric measurements of other sources. Racero et al. (2022) presented ESASky tools&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;to find these moving targets in Herschel data products. As a first step, we focused on the flux extraction of these serendipitous&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;observations of SSOs in Herschel/PACS measurements at 70, 100 and 160&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&amp;#956;&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;m.&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;We obtain far-infrared photometry on the&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;PACS maps, either by extracting the flux densities from the existing standard data products, or via re-reducing the PACS &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;maps in the co-moving frame of the target. Based on these scientifically very important far-IR flux densities, in combination&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;with already published IR detections (Szak &amp;#769;&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;ats et al., 2020), we perform radiometric studies to determine the objects&amp;#8217; physical&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;and thermal properties with unprecedented accuracy.&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;A natural continuation of our current work is the extension to SPIRE maps at 250, 350, and 500&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&amp;#956;&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;m, with a two-fold &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;aim.&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;First, to find serendipitous asteroids, extract new submm flux densities and flag sources in the SPIRE Point Source&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Catalog (Schulz et al., 2018) for possible contamination.&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;In addition, the dedicated SPIRE observations of asteroids for&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;various calibration activities are not yet published. As the SPIRE absolute photometry is connected to planet models, these &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;asteroid flux densities are of great value and will put strong constraints on their submm emissivity properties. All SPIRE&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;asteroid measurements were reprocessed and calibrated with the latest pipeline. The final maps are then used to extract high&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;quality IR/submm flux densities.&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;The flux densities are then added to the publicly available SBNAF Infrared Database&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;(Szak&amp;#225;&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;ts et al., 2020).&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;We collected the Herschel/SPIRE targeted asteroid measurements, and we went through the list of SPIRE observations &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;with potential serendipitous asteroid detections (from Racero et al. 2022). We only considered those, where the&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;isvisible&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;flag&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;was &amp;#8217;true&amp;#8217;. In a first step we verified that the photometry via the point source calibrated maps and the SSO calibrated maps&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;are in agreement. This is important because all the dedicated measurements were reprocessed in the object co-moving frame &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;and made available in the Herschel Science Archive, but not the serendipitous ones. Our tests confirmed that the two maps&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;give the same flux densities within the error bars, so there is no need to reprocess the serendipitous maps into the co-moving&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;frame. In a second part of the project, after making all flux densities available in the IR database, we perform radiometric&lt;/span&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;studies for individual asteroids. Depending on the a priori knowledge for a given object, we distinguish between the following&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;five categories: (1) mission targets, well-known/-studied objects; (2) objects with good-quality spin-shape solution and multi-&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;epoch/-mission thermal measurements; (3) good-quality spin-shape solution, but very limited or no thermal measurements &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;available; (4) no good-quality spin-shape solution, but sufficient multi-epoch/-mission thermal measurements available; (5)&lt;/span&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;no spin-shape solution and very limited thermal measurements available. In each of these five categories, the SPIRE (and &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;PACS) flux densities are important to obtain the object&amp;#8217;s emissivity properties, to constrain the thermal properties of the&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;surface or to establish basic radiometric size-albedo solutions.&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;We will present an overview of the new far-IR and sub-mm measurements (for about 17 dedicated program asteroids and &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;several different main-belt asteroids), the extracted flux densities, and applications for the different categories.&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;1050&quot; height=&quot;346&quot; /&gt;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Figure 1: The SPIRE maps for asteroid (10) Hygiea at 250, 350, and 500&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&amp;#956;&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;m, taken from a dedicated calibration sequence, &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;and processed in the object&amp;#8217;s co-moving frame.&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;&lt;img src=&quot;&quot; alt=&quot;&quot; width=&quot;1027&quot; height=&quot;282&quot; /&gt;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Figure 2: The SPIRE maps of the serendipitously seen asteroid (464) Megaira (marked by the green circles) at 250, 350, and &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;500&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&amp;#956;&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;m&lt;/span&gt;.&lt;/p&gt;