In the 170 years since its discovery, U Gem has been intensively studied as the prototypical cataclysmic binary star. Its massive white dwarf (WD) ( 1.2 Msun) is cannibalizing its 0.42 Msun red dwarf companion. The WD's resulting accreted hydrogen-rich envelope has previously undergone thermonuclear runaways seen as nova eruptions. These weekslong transient events brighten U Gem to m -3 and eject the accreted envelope ( 0.00001 Msun) at thousands of km/s. Ultraviolet observations show that the accreted envelope of U Gem's WD is greatly enhanced in nitrogen and depleted in carbon relative to solar composition, and that the WD's effective temperature is much hotter than that of most cataclysmic binary WDs. These suggest that U Gem underwent a classical nova eruption quite recently and should therefore still be surrounded by the ejecta of that event. Modeling of U Gem predicts a nova event 1000 years ago, and the existence of two concentric shells, each of order 1 degree in size, surrounding U Gem. We obtained deep narrowband H-alpha imaging of U Gem with the Condor Array Telescope. The two concentric H-alpha-bright shells that we find, centered on U Gem, may be the first-ever predicted old nova ejecta. A transient "guest star" in the asterism Shuiwei, recorded by Chinese imperial astrologers in November 829 CE is consistent with the timing and location of U Gem's last predicted nova eruption, but the transient's absence in Japanese and Korean records weighs against this suggestion.

Recurrent novae undergo thermonuclear-powered eruptions separated by less than 100 years, 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 parsec) super-remnants surrounding all recurrent novae; but only three examples are currently known. We report deep narrowband imaging and spectroscopy which has revealed a 70-parsec-diameter shell surrounding the frequently recurring nova RS Ophiuchi. We estimate the super-remnant mass to be 20 - 200 solar masses, 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 super-remnants. Our results support the prediction that ALL recurrent novae are surrounded by similar extended structures.

We used the Condor Array Telescope to obtain deep imaging observations through luminance broadband and He ii , [O iii ], He i , H α , [N ii ], and [S ii ] narrowband filters of an extended region of the M81 Group spanning ≈8 × 8 deg ^2 on 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.

We used the Condor Array Telescope to obtain deep imaging observations through the luminance broad-band and He II 468.6 nm, [O III] 500.7 nm, He I 587.5 nm, Hα, [N II] 658.4 nm, and [S II] 671.6 nm narrow-band filters of an extended region comprising 13 "Condor fields" spanning ≈ 8 × 8 deg^2 on the sky centered near M81 and M82. Here we describe the acquisition and processing of these observations, which together constitute unique very deep imaging observations of a large portion of the M81 Group through a complement of broad- and narrow-band filters. The images are characterized by an intricate web of faint, diffuse, continuum produced by starlight scattered from Galactic cirrus, and all prominent cirrus features identified in the broad-band image can also be identified in the narrow-band images. We subtracted the luminance image from the narrow-band images to leave more or less only line emission in the difference images, and we masked regions of the resulting images around stars at an isophotal limit. The difference images exhibit extensive extended structures of ionized gas in the direction of the M81 Group, from known galaxies of the M81 Group, clouds of gas, filamentary structures, and apparent or possible bubbles or shells. Specifically, the difference images show a remarkable filament known as the "Ursa Major Arc;" a remarkable network of criss-crossed filaments between M81 and NGC 2976, some of which intersect and overlap the Ursa Major Arc; and details of a "giant shell of ionized gas."

The diffuse Lyman-α glow of the cosmic web has long been predicted but has so far eluded direct detection over cosmologically significant volumes. We construct synthetic Lyman-α surface-brightness maps using five state-of-the-art hydrodynamic simulations (), modeling recombination, collisional excitation, star formation, and localized dust attenuation. Our study focuses on the redshift range 2.0<z<2.7, motivated by the numerous detailed studies of the COSMOS region. Significant variations are seen in the results obtained from these independent simulations. Using the Anderson-Darling statistic to probe these statistical differences, we demonstrate that a 5σ statistical detection of the total intergalactic and circumgalactic Lyman-α emission is achievable with current facilities at flux thresholds brighter than ∼ 8 × 10^-17 erg s^-1 cm^-2 arcsec^-2. Conversely, isolating the underlying low-density component of the cosmic web requires ultra-deep sensitivity, with the most optimistic simulation (IllustrisTNG) reaching a 5σ detection only for background noise levels below σ∼ 2 × 10^-19 erg s^-1 cm^-2 arcsec^-2. These quantitative limits validate the feasibility of ongoing wide-field narrow-band campaigns, opening a new era of empirical intergalactic cartography.

Classical nova eruptions result from thermonuclear-powered runaways in, and ejection of, the hydrogen-rich envelopes of white dwarf stars accreted from their close binary companions. Novae brighten to up to 1,000,000 solar luminosities, and recur thousands of times over their lifetimes spanning several billion years. Between eruptions, mass transfer from the donor star to the white dwarf proceeds via an accretion disk unless the white dwarf possesses a strong magnetic field which can partially or totally disrupt the disk. In that case, accretion is focussed by the white dwarf's magnetic field towards its magnetic poles. Optical spectroscopy and interferometric radio maps demonstrate the presence of bipolar jets, typically arcsec in angular size, and orders of magnitude smaller than one parsec in linear size, during the days to months after nova eruptions. These jets expel collimated matter from the white dwarfs in nova binary stars, but well-resolved images of them are lacking. Here we report the Condor telescope's detection of a hitherto unknown, highly resolved and braided jet, three degrees (at least 25 parsecs) in length. The jet originates at the white dwarf of the old nova GK Persei (nova Per 1901 CE). It precesses on a 3600 yr timescale, and must be at least 7200 years old. Detected across four decades of wavelength, the jet's ultimate energy source is likely the strong accretion shocks near the white dwarf's magnetic poles.

A century or less separates the thermonuclear-powered eruptions of recurrent novae in the hydrogen-rich envelopes of massive white dwarfs. The colliding ejecta of successive recurrent nova events are predicted to always generate very large (tens of parsecs) super-remnants; only two examples are currently known. T CrB offers an excellent opportunity to test this prediction. As it will almost certainly undergo its next, once-in 80-year recurrent nova event between 2024 and 2026, we carried out very deep narrowband and continuum imaging to search for the predicted, piled-up ejecta of the past millenia. While nothing is detected in continuum or narrowband [OIII] images, a 30-parsec-diameter, faint nebulosity surrounding T CrB is clearly present in deep Halpha, [NII] and [SII] narrowband Condor Array Telescope imagery. We predict that these newly detected nebulosities, as well as the recent ejecta that have not yet reached the super-remnant, are far too optically-thin to capture all but a tiny fraction of the photons emitted by RN flashes. We thus predict that fluorescent light echoes will NOT be detectable following the imminent nova flash of T CrB. Dust may be released by the T CrB red giant wind in pre-eruption outbursts, but we have no reliable estimates of its quantity or geometrical distribution. While we cannot predict the morphology or intensity of dust-induced continuum light echoes following the coming flash, we encourage multi-epoch Hubble Space Telescope optical imaging as well as James Webb Space Telescope infrared imaging of T CrB during the year after it erupts.

Most of the baryonic matter of the Universe resides in a highly-ionized gaseous intergalactic medium. This gas flows along dark-matter filaments toward galaxy superclusters, clusters, and groups until it pools around the galaxies into a circumgalactic medium. Eventually, the gas settles into the interstellar medium of the galaxies, where it fuels the successive generations of star formation that ultimately produce the stars and heavy elements that make up galaxies today. The gas has been studied for decades using absorption lines produced by Hydrogen and various ions of heavy elements in the spectra of background quasi-stellar objects (QSOs). But directly imaging the extremely faint glow of this "cosmic web" of intergalactic and circumgalactic gas has remained an elusive goal of observational cosmology. Some recent progress has been made by using imaging spectrographs to record high-redshift Lyα emission, although over only very narrow fields of view. Here we report direct images of intergalactic and circumgalactic gas in the distant Universe obtained using the Condor Array Telescope that we purposely built to reach extremely low-surface-brightness sensitivities over very wide fields of view. We show that these images directly detect and characterize the imprint of Lyα emission from the cosmic web at an overwhelming statistical significance. By stacking portions of the images centered on tens of thousands of galaxies of known redshift, we show that they also reveal extremely faint emission from H^0, C^3+, and Mg^+ and absorption from cosmic dust in the tenuous outskirts of the galaxies. Our results demonstrate that sensitive imaging observations can now detect and characterize emission (and absorption) from the cosmic web of intergalactic and circumgalactic gas (and dust).

The existence of a vast nova shell surrounding the prototypical dwarf nova Z Camelopardalis (Z Cam) proves that some old novae undergo metamorphosis to appear as dwarf novae thousands of years after a nova eruption. The expansion rates of ancient nova shells offer a way to constrain both the time between nova eruptions and the time for post-nova mass transfer rates to decrease significantly, simultaneously testing nova thermonuclear runaway models and hibernation theory. Previous limits on the expansion rate of part of the Z Cam shell constrain the inter-eruption time between Z Cam nova events to be $>$ 1300 years. Deeper narrow-band imaging of the ejecta of Z Cam with the Condor Array Telescope now reveals very low surface brightness areas of the remainder of the shell. A second, even fainter shell is also detected, concentric with and nearly three times the size of the"inner"shell. This is the first observational support of the prediction that concentric shells must surround the frequently-erupting novae of relatively massive white dwarfs. The Condor images extend our Z Cam imaging baseline to 15 years, yielding the inner shell's expansion rate as $v = 83 \pm 37$ km s$^{-1}$ at 23 degrees South of West, in excellent agreement with our 2012 prediction. This velocity corresponds to an approximate age of $t = 2672^{-817}_{+2102}$ yr. While consistent with the suggestion that the most recent nova eruption of Z Cam was the transient recorded by Chinese Imperial astrologers in the year 77 BCE, the age uncertainty is still too large to support or disprove a connection with Z Cam.

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 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.

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 Large Zenith Telescope is a 6 m optical telescope employing a rotating primary mirror coated with a film of liquid mercury. Located at an altitude of 400 m in the Coast Mountains of southwestern British Columbia, this telescope began regular operation in 2005 October. Equipped with a four-element Richardson prime-focus corrector and thinned 2048 x 2048 pixel drift-scanning CCD imaging camera, it is used for astronomical survey observations and also serves as an engineering test facility for further development of liquid-mirror technology. Built at a cost of less than $1 million dollars, it achieves an image quality and sensitivity comparable to that of a conventional telescope of equal aperture and is limited primarily by the astronomical quality of the site.

9:45 Invited Talk Aliens: The Scientific Search for Life on Other Planets Dr. Ben R. Oppenheimer (American Museum of Natural History) The discovery of life outside the solar system could arguably be one of the most important discoveries ever made. In fact, Astronomy and Biology are on the verge of a fascinating new convergence. Astrobiology, a new research initiative in several countries around the world, seeks to identify habitable planets outside our own solar system, and to identify the presence of life on such planets. However, to do this is extremely difficult, and chances are we won't be seeing little green men for quite a long time, even if they are out there. This lecture will attempt to explain the reality of the search for life in the universe, including a description of the techniques, what astrobiologists currently expect to find, and how all this might happen within a matter of two decades. 10:30 Contributed Talks I Photoionization Feedback in Low-Mass Galaxies at High Redshift Mark Dijkstra (Columbia U.) The cosmic ultraviolet (UV) ionizing background impacts the formation of dwarf galaxies in the low--redshift universe z ~ 3 by suppressing gas infall into galactic halos with circular velocities up to v_circ ~ 75 km/s. Using a one--dimensional, spherically symmetric hydrodynamics code (Thoul \& Weinberg 1995), we examine the effect of an ionizing background on low--mass galaxies forming at high redshifts (z>10). We find that the importance of photoionization feedback is greatly reduced, because (1) at high redshift, dwarf--galaxy sized objects can self-shield against the ionizing background, (2) collisional cooling processes at high redshift are more efficient, (3) the amplitude of the ionizing background at high redshift is lower, and (4) the ionizing radiation turns on when the perturbation that will become the dwarf galaxy has already grown to a substantial overdensity. We find that because of these reasons, gas can collect inside halos with circular velocities as low as v_circ ~ 10 km/s at z>10. This result has important implications for the reionization history of the universe. XMM Observation of Rich Clusters Dave Spiegel (Columbia U.) Rich clusters of galaxies can be clearly identified in x-ray images from Chandra and XMMNewton, consistent with their containing a large fraction of their baryonic mass as hot, highly ionized, diffuse gas. Some small groups of galaxies in the local universe have also been seen to contain a hot-gas component. Preliminary results from a 50 ksec XMM observation of a field with approximately 30 optically-identified galaxy-groups between redshift 0.1 and 0.6, however, indicate no spatial or spectral correlation between groups and x-ray emission. I will discuss the results and their possible importance. Radio and Millimeter observations of z~2 QSOs Andreea Petric (Columbia U.) & C. Carilli (NRAO) We present Very Large Array observations at 1.4 and 5 GHz of a sample of 16 quasi-stellar objects (QSOs) at z=1.78-2.71. These sources were chosen to have similar optical properties (MB, spectra) as samples of (z ≥ 3.7 QSOs) for which we have comparable (sub)millimeter (250 GHz) and centimeter observations. Half of the chosen quasars are bright at 250 or 350 GHz while the other half have not been detected at either of these frequencies. All eight FIR rich sources in our study were also detected at 1.4 GHz but only 3 of the FIR poor QSOs were barely detected at radio frequencies. This suggests a real physical difference between the FIR-luminous and FIR-quiet sources. If the super-massive black holes fueling these QSOs are accreting at Eddington rates and if the FIR is associated with star formation then we estimate that the spheroid and central-black hole grow on similar time-scales supporting the recent picture of their coevolution. Analyzing Current and Future Deep Field Surveys Stefan Gromoll & Kenneth M. Lanzetta (SBU) In 1995 the Hubble Deep Field provided the deepest image of the universe ever observed. The recent Great Observatories Origins Deep Survey (GOODS), while not as deep, covers 32 times the combined solid angle of the HDF and CDFS HST fields. The GOODS dataset is much more complex than the HDF data, consisting of 15--16 individual pointings covering the entire 10'x16' region, taken in 4 bandpasses (not including associated ground--based and SIRTF data). In addition, the data have been taken in five epochs, each seperated by 45 days, with the field of view rotated approximately 45 degrees between epochs. This amounts to a vast amount of fairly complex high quality deep imaging data which is available for analysis. The upcoming HST Ultra Deep Field survey (UDF), promises to be just as complex, and will extend around 1--2 magnitudes deeper than the HDF. Hence we identify two primary challenges with current and near future deep field surveys: to process such computationally large and complicated datasets, and to process them optimally to extract as much information as possible from these expensive and content--rich data. I will present our group's efforts to push the limits of photometric redshift and galaxy spectral type determination in these large datasets. 11:30 ASNY Graduate Student Prize Lecture Refining Chandra/ACIS Subpixel Event Repositioning Using a Backside Illuminated CCD Model Jingquang Li, Joel Kastner (RIT), Gregory Y. Prigozhin, Norbert S. Schulz (MIT) Subpixel event repositioning (SER) techniques have been demonstrated to significantly improve the already unprecedented spatial resolution of Chandra X-ray imaging with the Advanced CCD Imaging Spectrometer (ACIS). Chandra CCD SER techniques are based on the premise that the impact position of events can be refined, based on the distribution of charge among affected CCD pixels. ACIS SER models proposed thus far are restricted to corner split (3 and 4 pixel) events and assume that such events take place at the split-pixel corners. To improve the event-counting statistics, we modified the ACIS SER algorithms to include 2 pixel split events and single-pixel events, using refined estimates for photon impact locations. Furthermore, simulations that make use of a high-fidelity backside-illuminated (BI) CCD model demonstrate that mean photon impact positions for split events are energy dependent, leading to further modification of subpixel event locations according to event type and energy, for BI ACIS devices. Testing on Chandra CCD Xray observations of the Orion Nebula Cluster indicates that these modified SER algorithms further improve the spatial resolution of Chandra/ACIS, to the extent that the spreading in the spatial distribution of photons is dominated by the high-resolution mirror assembly, rather than by ACIS pixelization. 1: 30 Falling Bodies: The first of a new educational Physics video series Jill Linz (Skidmore College), co-written by Matt Christie (Skidmore ’02) and Kendrah Murphy (Skidmore ’03) Falling Bodies was written and produced in an effort to introduce physics into elementary schools. It is a comedic look at the historical development of our knowledge of how objects fall. Initially, members of the Skidmore Society of Physics Students traveled to a local school and performed this skit live to each sixth grade class. The sixth graders then recreated Galileo’s famous experiment on falling bodies using a water clock. While this program enjoyed great success, it was logistically complicated to perform on a regular basis. Therefore, we produced this movie version. In addition to the 20-minute movie shown today, there is an additional instructional video that explains to teachers how to perform the experiment in their classes. We hope this will aid teachers in introducing physics into their classes. 2:00 Invited Talk Jets from Young Stars Hsien Shang (Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan (ASIAA)) Recent observations have revealed that young stellar objects are associated with jet-like structures and Herbig-Haro objects emitting at wavelengths ranging from the optical to radio. These phenomena are similar in scale and morphology, and have mostly comparable energetics, dynamics, and kinematics. Probing such phenomena observed at various wavelengths with selfconsistent models of the physical and radiative processes arising within an inner disk wind, driven magnetocentrifugally from the circumstellar accretion disk, is a challenge for confronting theory and observation. I will discuss our efforts at modeling these jet phenomnea, and the diagnostic approach for comparing observations from optical to radio wavelengths. 2:45 Contributed Talks II Dynamical Masses of Young Stars in the Taurus Star Forming Region Gail Schaefer, M. Simon (SBU), E. Nelan, S.T. Holfeltz (STScI) We have been monitoring the orbital motion in the young binaries DF Tau and ZZ Tau and the hierarchical triple Elias 12 using the Fine Guidance Sensors on the Hubble Space Telescope and adaptive optics at the Keck Observatory (Schaefer et al. 2003, AJ, in press, astro-ph/0307020). Preliminary calculations show that the orbital parameters for these systems cannot yet be determined precisely because the orbital coverage spans only about 90 degrees in position angle. Nonetheless, the distribution of possible values for the period and semimajor axis already defines a useful estimate for the total mass in DF Tau and ZZ Tau, with values of 0.90 (+0.85/-0.35) Msun and 0.81 (+0.44/-0.25) Msun, respectively, at a fiducial distance of 140 pc. Mid-Infrared Imaging of Young Stellar Objects Ben Sargent (U. Rochester) With the launch of the Space Infrared Telescope Facility (SIRTF) comes the possibility of obtaining reliable infrared spectra, using SIRTF's Infrared Spectrograph (IRS), of sources which are relatively faint at infrared wavelengths. In anticipation of the success of the IRS, an observation/spectrography program, IRS_Disks, has been prepared, in which images and spectra of numerous Young Stellar Obje