A small number of double-lobed radio galaxies (17 from our own census of the literature) show an additional pair of low surface brightness 'wings', thus forming an overall 'X'-shaped appearance. The origin of the wings in these radio sources is unclear. They may be the result of back-flowing plasma from the currently active radio lobes into an asymmetric medium surrounding the active nucleus, which would make these ideal systems in which to study thermal/non-thermal plasma interactions in extragalactic radio sources. Another possibility is that the wings are the aging radio lobes left over after a (rapid) realignment of the central supermassive black-hole/accretion disk system due perhaps to a merger. Generally, these models are not well tested; with the small number of known examples, previous works focused on detailed case studies of selected sources with little attempt at a systematic study of a large sample. Using the VLA-FIRST survey database, we are compiling a large sample of winged and X-shaped radio sources for such studies. As a first step toward this goal, an initial sample of 100 new candidate objects of this type are presented in this paper. The search process is described, optical identifications from available literature data, and basic radio data are presented. From the limited resolution FIRST images (∼5 ′′ ), we can already confidently classify a sufficient number of these objects as having the characteristic wing lengths >80% of the active lobes to more than double the number of known X-shaped radio sources. We have also included as candidates, radio sources with shorter wings (<80% wing to lobe length ratios), or simply 'winged' sources, as it is probable that projection effects are important. Finally, among the candidates are four quasars (z=0.37 to 0.84), and several have morphologies suggestive of Fanaroff-Riley type-I (low-power) radio galaxies. While followup observations are necessary to confirm these identifications, this stresses the importance of source orientation and imaging limitations in finding these enigmatic objects.

The composition of comets in the Solar System come in multiple groups thought to encode information about their formation in different regions of the outer protosolar disk. The recent discovery of the second interstellar object, 2I/Borisov, allows for spectroscopic investigations into its gas content and a preliminary classification of it within the Solar System comet taxonomies to test the applicability of planetesimal formation models to other stellar systems. We present spectroscopic and imaging observations from 2019 September 20th through October 26th from the Bok, MMT, and LBT telescopes. We identify CN in the comet's spectrum and set precise upper limits on the abundance of C2 on all dates. We use a Haser model to convert our integrated fluxes to production rates and find Q(CN) = 5.0 +/-2.0 * 10^24 mol/s on September 20 th and Q(CN) = (1.1 -1.9) * 10^24 mols/s on later dates, both consistent with contemporaneous observations. We set our lowest upper limit on a C2 production rate, Q(C2) < 1.6 10^23 mols/s on October 10th. The measured ratio upper limit for that date Q(C2)/Q(CN) < 0.095 indicates that 2I/Borisov is strongly in the (carbon chain) 'depleted' taxonomic group. The only comparable Solar System comets have detected ratios near this limit, making 2I/Borisov statistically likely to be more depleted than any known comet. Most 'depleted' comets are Jupiter Family Comets, perhaps indicating a similarity in formation conditions between the most depleted of the JFCs and 2I/Borisov. More work is needed to understand the applicability of our knowledge of Solar System comet taxonomies onto interstellar objects and we discuss future work that could help to clarify the usefulness of the approach.

Linking meteorites to source regions in the main asteroid belt is important for understanding the conditions under which their parent bodies formed. Ordinary chondrites are the most abundant class of meteorites on Earth, totaling 86% of all collected samples. Some S-type asteroids/families have been proposed as sources for the three different (H, L, and LL) types of ordinary chondrites with Hebe, Agnia, Merxia, and Koronis families being the source for H chondrites, Gefion for H/L chondrites, and Flora family for LL chondrites. However, the composition and meteorite affinity of several large S-type main belt asteroids remains unconstrained leaving the possibility of additional source regions for ordinary chondrite meteorites. Here we investigate the surface composition of three large S-type asteroids, (3) Juno, (7) Iris, and (25) Phocaea, using their near-infrared spectra (0.7-2.55 μm) to identify the parent body of the H chondrites. We use a Bayesian inference model to confirm the meteorite analogs of the three asteroids. Based on our Bayes classifier we find the following analogs and probabilities: Juno is likely H chondrite (89%), Iris is likely LL chondrite (97.5%), and Phocaea is likely H chondrite (98.6%). While Phocaea has the highest probability of being an H chondrite, it is dynamically unlikely to deliver material to near-Earth space. While Juno has spectral properties similar to H chondrites, its family is unlikely to produce sizeable H-chondrite-type near-Earth objects (NEOs). If Juno is the primary source of H chondrite meteorites, it suggests that an additional source is needed to explain the H-chondrite-type NEOs.

Although numerous white dwarf stars host dusty debris disks, the temperature distribution of these stars differs significantly from the white dwarf population as a whole. Dusty debris disks exist exclusively around white dwarfs cooler than 27,000 K. This is all the more enigmatic given that the formation processes of dusty debris disks should favor younger, hotter white dwarfs, which likely host more dynamically unstable planetary systems. Here we apply a sophisticated material sublimation model to white dwarf systems to show that these statistics are actually a natural result of the interplay of thermal and tidal forces and how they define the circumstellar regions where dusty debris disks can form. We demonstrate that these processes tend to prevent stability against both sublimative destruction and reaccretion into planetesimals for rocky materials until white dwarfs cool to below ∼25,000–32,000 K, in agreement with the observed limit of ∼27,000 K. For pure water ice, this critical temperature is less than 2700 K (requiring a cooling age older the universe); this precludes pure water ice–rich debris disks forming through the accepted two-step mechanism. The critical temperature is size-dependent; more massive white dwarfs could potentially host dusty debris disks at warmer temperatures. Our model suggests that the location of the disks within the PG 0010+280, GD 56, GD 362, and PG 1541+651 systems are consistent with a forsterite-dominated olivine composition. We also find that very cool white dwarfs may simultaneously host multiple, independently formed dusty debris disks, consistent with observations of the LSPM J0207+3331 system.