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Benjamin Eagles
Benjamin Eagles

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I'm not sure what you want me to do. The devices is registered in Azure. I can see the device, I can see the groups it belongs to. I even gets apps and configurations distributed through Azure-groups. So everything seems to work, except that the "Activity" says "N/A". When it comes to the personal Android-devices you can see the latest activity.

with high priority type = 2 days no activity should trigger an email to the assignee, and with medium type = 4 days no activity should trigger the email and so on. and another notification to project lead when high priority type exceed 4 days with no activity and so on

Figure 1. Perihelion distance vs. heliocentric distance of 13 Centaurs studied in this work compared to known active Centaurs and JFC Centaurs, as well as the known Centaur population. All known active Centaurs reside within the interval where the crystallization of AWI is possible. Our targets are distributed both within and beyond the crystallization interval. A magenta star marks the position of 167P/CINEOS, which shares a similar orbit and heliocentric position at the time of activity to those of one of the Centaurs in our sample, 2014 OX393.

Therefore, considering the wide range of heliocentric distances at which Centaurs exhibit comae, the Centaur activity likely has more sources than just sublimation of surface volatiles, and these sources may be triggered by multiple mechanisms, some of which could be different from those acting in regular comets.

It has been suggested that activity on Centaurs and some comets at large heliocentric distances is driven by the crystallization of amorphous water ice (AWI), which is porous and can contain molecules of supervolatile ices trapped in the AWI during the condensation (Notesco & Bar-Nun 1996; Jewitt 2009; Shi & Ma 2015). When the parent body enters a warmer environment, a crystallization front starts propagating into the interior of the body, releasing trapped gas molecules, which then start to loft dust grains at temperatures much lower than necessary for sublimation of crystalline water ice. AWI has been detected by in situ observation of the Galilean moons of Jupiter (Hansen & McCord 2004); however, the presence of AWI has never been observationally confirmed on small bodies in the solar system (Lisse et al. 2013).

In this work we have observed and analyzed 13 Centaurs discovered in the Pan-STARRS1 detection database (Weryk et al. 2016). All our targets have well-defined orbits with orbital arcs spanning almost a decade. Our investigation consisted of three steps: (1) analysis of images taken with Gemini-N to search for comet-like activity, (2) a search of archival images from the Dark Energy Camera (DECam) to look for traces of activity in the past, (3) thermal modeling to examine surface temperatures as a function of orbital parameters and object size to put upper limits on sublimative gas production from volatile species potentially present on the surface, and (4) numerical integrations to inspect the orbital histories of objects in our sample.

Our target list consisted of 13 Centaurs selected from a sample of 29 new Centaur discoveries from the Pan-STARRS1 detection catalog (Weryk et al. 2016) that were observable in the second half of 2017 from the Northern Hemisphere and were within Gemini-N observation limits. We included objects with perihelia spanning the entire Centaur region and crossing the putative AWI crystallization heliocentric distance interval (Jewitt 2009; Guilbert-Lepoutre 2012). Most of the known active Centaurs were discovered close to perihelion and were active at discovery. We therefore primarily selected targets close to perihelion to ensure the best conditions for observing possible activity. As of 2021 June none of our targets have been the subject of characterization by other works.

Figures 1 and 2 show that our targets cover a wide range of orbital elements typical for Centaurs and stay clear of the region often referred to as the "JFC Gateway," a temporary low-eccentricity region exterior to Jupiter through which the majority of Centaurs bound to become JFCs pass (Sarid et al. 2019; Steckloff et al. 2020). In contrary, most objects in our sample have perihelia near the upper limit of the AWI crystallization zone because the data-mining algorithm applied to the Pan-STARRS1 detection database was tuned to find objects beyond Neptune and the discovered Centaurs were mostly a by-product of that search (Weryk et al. 2016). It can also be seen that the activity in Centaurs does not seem to be related to any preferential eccentricity or inclination ranges, but instead their perihelion distances appear to be the main constraint.

We have also calculated Tisserand's parameter with respect to Saturn and Uranus, TS and TU , respectively, and Table 2 shows that about half of our targets are likely more influenced by the outer planets than Jupiter. The current values of TJ of our targets and other bodies in the region are plotted against their perihelion distance and are shown in Figure 3. Again, we do not note any apparent correlation between activity and TJ .

Figure 5. Postage stamp cutouts from stacked images of 13 Centaurs observed in this work. The spatial dimensions of each stamp are 30'' 30'', and each stamp is centered on the object, with north up and east to the left. None of the objects showed obvious visual signs of activity, a conclusion supported by the SBP analysis (see Section 3.1).

In order to search for activity in our observational data, we first identified the correct object in each star field by "blinking" the individual images and visually inspecting each one for extended surface brightness features moving along with the source. We then stacked the images using standard IRAF routines to increase the S/N. All our targets appeared stellar based on simple visual inspection, as can be seen in Figure 5.

In our analysis of the thermal environment of the inspected Centaurs we were focusing on two possible activity sources: the solar-driven sublimation of surface volatiles, and the crystallization of AWI capable of releasing trapped gases. Multiple volatile species have been observationally detected in active Centaurs (e.g., Senay & Jewitt 1994; Womack & Stern 1997; Wierzchos et al. 2017; Womack et al. 2017), while there is no direct evidence of the presence of AWI (Lisse et al. 2013) on Centaur surfaces. It has to be noted that, due to their distance and their corresponding faintness, the detection of any volatile species on Centaurs sized similarly to our sample is extremely challenging (Kareta et al. 2021).

To assess the plausibility of activity driven by sublimation of surface volatile deposits, we have computed the theoretical maximal sublimation rates for the three most common volatiles found in comets, CO, CO2, and H2O, for each of our targets at their observed heliocentric distances. We used the thermal model described by Steckloff et al. (2015), which assumes a spherical graybody covered entirely in the pure volatile species of interest, with an albedo of approximately 4% and emissivity of 0.9. The model calculates the dynamic sublimation pressure and the sublimative mass-loss rate across the surface of a planetary body by numerically solving for the equilibrium temperature that balances incident solar energy with radiative and sublimative heat loss. The model integrates over the entire surface of the spherical nucleus and accounts for lower sunlight intensity toward the terminator due to increasing solar incidence angles, assuming that all sunlight is used to sublime volatiles. This model thus estimates maximal production rates capable from solar-driven activity.

All above implies that the apparently inactive/dormant Centaurs orbiting within the AWI crystallization zone have probably already depleted their surface volatiles, since the average CO sublimation loss in the region is several meters per orbit (Li et al. 2020), and the CO2-driven activity would be visible, but they could still contain subsurface pockets of volatiles and AWI buried under the dust crust. A sudden rapid orbital change pushing the perihelion closer to the Sun could jump-start the crystallization front, which will move rapidly releasing trapped gas until enough pressure builds up to cause a landslide or opens a sinkhole exposing subsurface layers. This process could lead to large-scale outgassing and/or outburst, possibly with a significant lag, as was observed in several active Centaurs (Mazzotta Epifani et al. 2006) and also in quasi-Hilda P/2010 H2 (Vales) (Jewitt & Kim 2020). Such rapid release of gases could also eject a large boulder or a chunk of the parent body that can continue to disintegrate, as has been likely observed during a dramatic outburst of 174P/Echeclus in 2005, where the the nucleus and coma brightness peaks were spatially separated (Bauer et al. 2008; Rousselot 2008; Kareta et al. 2019). As the crystallization front moves through the body, it could keep building the pressure pockets and create openings throughout the surface even far away from perihelion, and in subsequent orbital passages until the volatile deposits in each pocket are depleted.

It should be noted that our calculated values should only be used as order-of-magnitude estimates given that there are no direct simultaneous measurements of gas and dust mass loss from an active Centaur. The fdg ratio can change depending on the Centaur and whether the mass loss is a product of a quiescent activity or an outburst (Fernández et al. 2020). A fresh sinkhole opening up and causing an outburst could be much dustier than a steady-state outgassing event diffusing through surface regolith. For example, Wierzchos & Womack (2020) has shown that in the case of 29P several CO outbursts did not have a corresponding dust outburst. There is currently a real lack of knowledge of the gas-to-dust ratio of Centaurs owing to observational limitations, which will be hopefully addressed and alleviated with future works using JWST (Kelley et al. 2016), but such rigorous analysis is beyond the scope of this paper. 041b061a72


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