Papers by Damian Christian
Solar Physics, Nov 30, 2023
The solar physics community is entering a golden era that is ripe with next-generation ground-and... more The solar physics community is entering a golden era that is ripe with next-generation ground-and space-based facilities, advanced spectral inversion techniques, and realistic simulations that are becoming more computationally streamlined and efficient. With everincreasing resolving power stemming from the newest observational telescopes, it becomes more challenging to obtain (near-)simultaneous measurements at high spatial, temporal and spectral resolutions, while operating at the diffraction limit of these new facilities. Hence, in recent years there has been increased interest in the capabilities integral field units (IFUs) offer towards obtaining the trifecta of high spatial, temporal and spectral resolutions contemporaneously. To date, IFUs developed for solar physics research have focused on mid-optical and infrared measurements. Here, we present an IFU prototype that has been designed for operation within the near-ultraviolet to mid-optical wavelength range, which enables key spectral lines (e.g., Ca II H/K, Hβ, Sr II, Na I D 1 /D 2 , etc.) to be studied, hence providing additional spectral coverage to the instrument suites developed to date. The IFU was constructed as a low-budget proof-of-concept for the upcoming 2 m class Indian National Large Solar Telescope and employs circular cross-section fibres to guide light into a Czerny-Turner configuration spectrograph, with the resulting spectra captured using a high quantum efficiency scientific CMOS camera. Mapping of each input fibre allows for the reconstruction of two-dimensional spectral images, with frame rates exceeding 20 s −1 possible while operating in a non-polarimetric configuration. Initial commissioning of the instrument was performed at the Dunn Solar Telescope, USA, during August 2022. The science verification data presented here highlights the suitability of fibre-fed IFUs operating at near-ultraviolet wavelengths for solar physics research. Importantly, the successful demonstration of this type of instrument paves the way for further technological developments to make a future variant suitable for upcoming ground-based and space-borne telescope facilities.
Comet nuclei are remnants from the planet formation era but cannot be observed directly from Eart... more Comet nuclei are remnants from the planet formation era but cannot be observed directly from Earth. When they approach the Sun a cloud of gas dust obscures their nuclei, and their properties must be inferred from gas and dust surrounding them. Understanding the connection between the coma and nucleus is therefore critical. Comet 46P/Wirtanen passed Earth with an historic closest approach distance of 0.077 au (12 million km) on Dec. 16, 2018. Its apparition was widely anticipated by planetary scientists and was the target of a world-wide observing campaign. Studies of comet Wirtanen around the time of its close approach to Earth provided spatial resolutions high enough to permit valuable comparisons to the Rosetta observations of 67P/Churyumov-Gerasimenko and the Deep Impact/EPOXI fly-by results of 103P/Hartley 2. In this contribution, we will summarize the preliminary results from our global campaign that combined telescopes in and around Earth to characterize the physical and chemi...
The Planetary Science Journal, 2021
In this paper, we present an analysis of X-ray and optical/ultraviolet (UV) data from the favorab... more In this paper, we present an analysis of X-ray and optical/ultraviolet (UV) data from the favorable (Δ ∼ 0.077 au) 2018 apparition of comet 46P/Wirtanen. The comet was observed during three different epochs (before, during, and after perihelion) over a 1.5 month period using the X-Ray Telescope (XRT) and Ultraviolet and Optical Telescope (UVOT) instruments on board the Neil Gehrels Swift Observatory and the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-ray Observatory. We clearly detected the comet’s charge exchange-induced emission during the first two epochs (F x = (11.2 ± 0.8) and (6.9 ± 0.5) × 10−13 erg cm−2 s−1, respectively), while only an upper limit on the flux could be placed for the third epoch (F x < 1.38 × 10−13 erg cm−2 s−1). As such, 46P/Wirtanen is one of the least luminous comets to be detected in X-rays. X-ray emission from the charge exchange between solar wind ions and the neutrals in the coma were analyzed against the water-production rate (S...
Research in Astronomy and Astrophysics, 2019
We present multi-wavelength observations of an M-class flare (M3.9) that occurred on 2014 June 11... more We present multi-wavelength observations of an M-class flare (M3.9) that occurred on 2014 June 11. Our observations were conducted with the Dunn Solar Telescope (DST), adaptive optics, the multi-camera system ROSA (Rapid Oscillations in Solar Atmosphere) and new HARDcam (Hydrogen-Alpha Rapid Dynamics) camera in various wavelengths, such as Ca II K, Mg I b 2 (at 5172.7Å), and Hα narrow-band, and G-band continuum filters.
The Astronomical Journal, 2002
The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually c... more The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic survey that will eventually cover approximately one-quarter of the celestial sphere and collect spectra of %10 6 galaxies, 100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001 June, the SDSS released to the general astronomical community its early data release, roughly 462 deg 2 of imaging data including almost 14 million detected objects and 54,008 follow-up spectra. The imaging data were collected in drift-scan mode in five bandpasses (u, g, r, i, and z); our 95% completeness limits for stars are 22.0, 22.2, 22.2, 21.3, and 20.5, respectively. The photometric calibration is reproducible to 5%, 3%, 3%, 3%, and 5%, respectively. The spectra are flux-and wavelength-calibrated, with 4096 pixels from 3800 to 9200 Å at R % 1800. We present the means by which these data are distributed to the astronomical community, descriptions of the hardware used to obtain the data, the software used for processing the data, the measured quantities for each observed object, and an overview of the properties of this data set.
The Astronomical Journal, 2017
Using Chandra, we have obtained imaging X-ray spectroscopy of the 10-16 Myr old F-star binary HD ... more Using Chandra, we have obtained imaging X-ray spectroscopy of the 10-16 Myr old F-star binary HD 113766. We individually resolve the 1 4 separation binary components for the first time in the X-ray and find a total 0.3-2.0 keV luminosity of 2.2×10 29 erg s −1 , consistent with previous RASS estimates. We find emission from the easternmost, infrared-bright, dusty member HD 113766A to be only ∼10% that of the western, infrared-faint member HD 113766B. There is no evidence for a 3rd late-type stellar or substellar member of HD 113766 with L x >6×10 25 erg s −1 within 2′ of the binary pair. The ratio of the two stars' X-ray luminosity is consistent with their assignments as F2V and F6V by Pecaut et al. The emission is soft for both stars, kT Apec =0.30-0.50 keV, suggesting X-rays produced by stellar rotation and/or convection in young dynamos, but not accretion or outflow shocks, which we rule out. A possible 2.8±0.15 (2σ) hr modulation in the HD 113766B X-ray emission is seen, but at very low confidence and of unknown provenance. Stellar wind drag models corresponding to L x ∼2×10 29 erg s −1 argue for a 1 mm dust particle lifetime around HD 113766B of only ∼90,0000 years, suggesting that dust around HD 113766B is quickly removed, whereas 1 mm sized dust around HD 113766A can survive for >1.5×10 6 years. At 10 28-10 29 erg s −1 X-ray luminosity, astrobiologically important effects, like dust warming and X-ray photolytic organic synthesis, are likely for any circumstellar material in the HD 113766 systems.
Universe
By exploring more than sixty thousand quasars from the Sloan Digital Sky Survey Data Release 5, S... more By exploring more than sixty thousand quasars from the Sloan Digital Sky Survey Data Release 5, Steinhardt & Elvis discovered a sub-Eddington boundary and a redshift-dependent drop-off at higher black hole mass, possible clues to the growth history of massive black holes. Our contribution to this special issue of Universe amounts to an application of a model for black hole accretion and jet formation to these observations. For illustrative purposes, we include ~100,000 data points from the Sloan Digital Sky Survey Data Release 7 where the sub-Eddington boundary is also visible and propose a theoretical picture that explains these features. By appealing to thin disk theory and both the lower accretion efficiency and the time evolution of jetted quasars compared to non-jetted quasars in our “gap paradigm”, we explain two features of the sub-Eddington boundary. First, we show that a drop-off on the quasar mass-luminosity plane for larger black hole mass occurs at all redshifts. But the...
International Astronomical Union Colloquium
We present EUVE survey results for moderate column directions containing known low-mass X-ray bin... more We present EUVE survey results for moderate column directions containing known low-mass X-ray binaries (LMXB). We derive Lexan band (100 Å) count rates and upper limits for nearly 40 LMXB chosen generally with EB-V ≤ 0.3. Detections include Sco X-1, Her X-1, and the GRO transient CJ0422+32. Super soft sources in the LMC yield 3 σ upper limits of ≤ 10 counts ks−1. The extrapolation of two component spectral models (such as blackbody plus thermal bremsstrahlung), are in agreement with the survey upper limits. Contemporary LMXB spectral models, which involve Comptonization in an inner disk corona, predict a large flux of EUV photons. If the above model is correct in the EUV, such a component could be detected in source with low column densities. We argue that additional intrasystem column hampers its detection.
The Astrophysical Journal
Over the past number of years, great strides have been made in identifying the various low-order ... more Over the past number of years, great strides have been made in identifying the various low-order magnetohydrodynamic wave modes observable in a number of magnetic structures found within the solar atmosphere. However, one aspect of these modes that has remained elusive, until now, is their designation as either surface or body modes. This property has significant implications for how these modes transfer energy from the waveguide to the surrounding plasma. Here, for the first time to our knowledge, we present conclusive, direct evidence of these wave characteristics in numerous pores that were observed to support sausage modes. As well as outlining methods to detect these modes in observations, we make estimates of the energies associated with each mode. We find surface modes more frequently in the data, as well as that surface modes appear to carry more energy than those displaying signatures of body modes. We find frequencies in the range of ∼2-12mHz, with body modes as high as 11mHz, but we do not find surface modes above 10mHz. It is expected that the techniques we have applied will help researchers search for surface and body signatures in other modes and in differing structures from those presented here.
Bulletin of the American Astronomical Society, Dec 1, 1995
Bulletin of the American Astronomical Society, May 1, 1996
The Extreme Ultraviolet Explorer (EUVE ) has three scanning telescopes that observe in a directio... more The Extreme Ultraviolet Explorer (EUVE ) has three scanning telescopes that observe in a direction perpendicular to that of the primary guest observer (GO) telescope---the Deep Survey/Spectrometer (DS/S). During the first 6 months of the EUVE mission, the scanning telescopes were used to conduct an all-sky survey consisting of short exposures ( ~ 500 s) of the entire sky between
Euve Proposal, 1996
We propose EUVE Deep Survey lexan band observations of the new CV EUVE J2115-586. The primary obj... more We propose EUVE Deep Survey lexan band observations of the new CV EUVE J2115-586. The primary objective is to obtain Deep Survey light curve to constrain the systems accretion geometry and further classify this system. In addition, if the source is in a particularly bright high-state we may be able to search for tens of second QPOs observed for several AM Hers.
NGC 281 (a.k.a. the Pac Man Nebula) is a complex region of star formation. At a distance of about... more NGC 281 (a.k.a. the Pac Man Nebula) is a complex region of star formation. At a distance of about 3 kpc is lies a remarkable 300 pc above the galactic plane. Apparently triggered by a supernova that occurred 6 Myr ago, it includes at least 3 separate but related sites of star formation within 4 pc. The oldest regions includes
The field of multi-wavelength astronomy has blossomed in recent years as more and more satellite ... more The field of multi-wavelength astronomy has blossomed in recent years as more and more satellite are launched. Astronomers are currently able to observe at wavelengths ranging from optical to gamma ray with space-based observatories and at optical, infrared, and radio wavelengths with ground-based telescopes. In early 1995, recognizing the enhanced science return that coordinated observations can produce, the EUVE, XTE,
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Papers by Damian Christian