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Abstract Recurrent novae undergo thermonuclear-powered eruptions separated by less than 100 yr, enabled by subgiant or red giant donors transferring hydrogen-rich matter at very high rates onto their massive white dwarf companions. The most rapidly moving parts of envelopes ejected in successive recurrent nova events are predicted to overtake and collide with the slowest ejecta of the previous eruption, leading to the buildup of vast (∼10–100 pc) superremnants surrounding all recurrent novae, but only three examples are currently known. We report deep narrowband imaging and spectroscopy, which have revealed a ∼70 pc diameter shell surrounding the frequently recurring nova RS Ophiuchi. We estimate the superremnant mass to be ∼20–200M_⊙, expanding at a few tens of km/s, with an age of order 50–100 kyr. Its extremely low surface brightness and large angular size help explain the hitherto surprising absence of nova superremnants. Our results support the prediction that all recurrent novae are surrounded by similar extended structures. 

Abstract We used the Condor Array Telescope to obtain deep imaging observations through luminance broadband and Heii, [Oiii], Hei, Hα, [Nii], and [Sii] narrowband filters of an extended region of the M81 Group spanning ≈8 × 8 deg²on the sky centered near M81 and M82. Here, we report aspects of these observations that are specifically related to (1) a remarkable filament known as the “Ursa Major Arc” that stretches ≈30° across the sky roughly in the direction of Ursa Major, (2) a “giant shell of ionized gas” that stretches ≈0.8 deg across the sky located ≈0.6 deg northwest of M82, and (3) a remarkable network of ionized gaseous filaments revealed by the new Condor observations that appear to connect the arc, the shell, and various galaxies of the M81 Group and, by extension, the group itself. We measure flux ratios between the various ions to help to distinguish photoionized from shock-ionized gas, and we find that the flux ratios of the arc and shell are not indicative of shock ionization. This provides strong evidence against a previous interpretation of the arc as an interstellar shock produced by an unrecognized supernova. We suggest that all of these objects, including the arc, are associated with the M81 Group and are located at roughly the distance (≈3.6 Mpc) of M81, that the arc is an intergalactic filament, and that the objects are associated with the low-redshift cosmic web. 

ABSTRACT We used the Condor array telescope to obtain deep imaging observations through the luminance filter of the entirety of the NGC 5866 Group, including a very extended region surrounding the galaxy NGC 5907 and its stellar stream. We find that the stellar stream consists of a single curved structure that stretches 220 kpc from a brighter eastern stream to a fainter western stream that bends to the north and then curls back toward the galaxy. This result runs contrary to a previous claim of a second loop of the stellar stream but is consistent with another previous description of the overall morphology of the stream. We further find that: (1) an extension of the western stream appears to bifurcate near its apex, (2) there is an apparent gap of ≈6 kpc in the western stream due east of the galaxy, (3) contrary to a previous claim, there is no evidence of the remnant of a progenitor galaxy within the eastern stream, although (4) there are many other possible progenitor galaxies, (5) there is another structure that, if it is at the distance of the galaxy, stretches 240 kpc and contains two very large, very low-surface-brightness ‘patches’ of emission, one of which was noted previously and another of which was not. We note the number and variety of stellar streams in the vicinity of NGC 5907 and the apparent gap in the western stream, which may be indicative of a dark sub-halo or satellite in the vicinity of the galaxy. 

ABSTRACT Just 10 recurrent novae (RNe) – which erupt repeatedly on time-scales shorter than one century – are known in our Galaxy. The most extreme RN known (located in the Andromeda galaxy), M31N 2008-12a, undergoes a nova eruption every year, and is surrounded by a vast nova ‘super-remnant’, 134 pc in extent. Simulations predict that all RNe should be surrounded by similar vast shells, but previous searches have failed to detect them. KT Eri has recently been suggested to be a RN, and we have used the Condor Array Telescope to image its environs through multiple narrow-band filters. We report the existence of a large (∼50-pc diameter), H $$\, \alpha$$-bright shell centred on KT Eri, exactly as predicted. This strongly supports the claim that KT Eri is the 11th Galactic recurrent nova, and only the second nova known to be surrounded by a super-remnant. SALT spectra of the super-remnant demonstrate that its velocity width is consistent with that of M31-2008-12a. 

Abstract The “Condor Array Telescope” or “Condor” is a high-performance “array telescope” comprised of six apochromatic refracting telescopes of objective diameter 180 mm, each equipped with a large-format, very low-read-noise (≈1.2 e − ), very rapid-read-time (<1 s) CMOS camera. Condor is located at a very dark astronomical site in the southwest corner of New Mexico, at the Dark Sky New Mexico observatory near Animas, roughly midway between (and more than 150 km from either) Tucson and El Paso. Condor enjoys a wide field of view (2.29 × 1.53 deg 2 or 3.50 deg 2 ), is optimized for measuring both point sources and extended, very low-surface-brightness features, and for broad-band images can operate at a cadence of 60 s (or even less) while remaining sky-noise limited with a duty cycle near 100%. In its normal mode of operation, Condor obtains broad-band exposures of exposure time 60 s over dwell times spanning dozens or hundreds of hours. In this way, Condor builds up deep, sensitive images while simultaneously monitoring tens or hundreds of thousands of point sources per field at a cadence of 60 s. Condor is also equipped with diffraction gratings and with a set of He ii 468.6 nm, [O iii ] 500.7 nm, He i 587.5 nm, H α 656.3 nm, [N ii ] 658.4 nm, and [S ii ] 671.6 nm narrow-band filters, allowing it to address a variety of broad- and narrow-band science issues. Given its unique capabilities, Condor can access regions of “astronomical discovery space” that have never before been studied. Here we introduce Condor and describe various aspects of its performance. 

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. These new methods will become increasingly important in the coming years as the volume of survey data continues to increase, and as the degeneracy between predictions of different physical models grows. There are several perspectives on the divergences between the values of cosmological parameters, such as the model-independent probes in the late Universe and model-dependent measurements in the early Universe, which we cover at length. The White Paper closes with a number of recommendations for the community to focus on for the upcoming decade of observational cosmology, statistical data analysis, and fundamental physics developments