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Articles 91 - 120 of 177
Full-Text Articles in Stars, Interstellar Medium and the Galaxy
A Multiwavelength Analysis Of The Halo Planetary Nebula Dddm‐1, R. B. C. Henry, K. B. Kwitter, R. J. Dufour, J. N. Skinner
A Multiwavelength Analysis Of The Halo Planetary Nebula Dddm‐1, R. B. C. Henry, K. B. Kwitter, R. J. Dufour, J. N. Skinner
Dartmouth Scholarship
We present new HST optical imagery as well as new UV and IR spectroscopic data obtained with the Hubble Space Telescope and Spitzer Space Telescope, respectively, of the halo planetary nebula DdDm-1. For the first time we present a resolved image of this object, which indicates that the morphology of DdDm-1 can be described as two orthogonal elliptical components in the central part surrounded by an extended halo. The extent of the emission is somewhat larger than was previously reported in the literature. We combine the spectral data with our own previously published optical measurements to derive nebular abundances …
Deep Advanced Camera For Surveys Imaging In The Globular Cluster Ngc 6397: The Cluster Color-Magnitude Diagram And Luminosity Function, Harvey B. Richer, Aaron Dotter, Jarrod Hurley, Jay Anderson
Deep Advanced Camera For Surveys Imaging In The Globular Cluster Ngc 6397: The Cluster Color-Magnitude Diagram And Luminosity Function, Harvey B. Richer, Aaron Dotter, Jarrod Hurley, Jay Anderson
Dartmouth Scholarship
We present the color-magnitude diagram (CMD) from deep Hubble Space Telescope imaging in the globular cluster NGC 6397. The Advanced Camera for Surveys (ACS) was used for 126 orbits to image a single field in two colors (F814W, F606W) 5' SE of the cluster center. The field observed overlaps that of archival WFPC2 data from 1994 and 1997 which were used to proper motion (PM) clean the data. Applying the PM corrections produces a remarkably clean CMD which reveals a number of features never seen before in a globular cluster CMD. In our field, the main-sequence stars appeared to terminate …
The Nature Of The Ultraluminous Oxygen‐Rich Supernova Remnant In Ngc 4449, Dan Milisavljevic, Robert A. Fesen
The Nature Of The Ultraluminous Oxygen‐Rich Supernova Remnant In Ngc 4449, Dan Milisavljevic, Robert A. Fesen
Dartmouth Scholarship
Optical images and spectra, both ground based and taken by Hubble Space Telescope (HST), of the young, luminous O-rich supernova remnant in the irregular galaxy NGC 4449 are presented. HST images of the remnant and its local region were obtained with the ACS/WFC using filters F435W, F555W, F814W (B, V, and I, respectively), F502N ([O III]), F658N (Hα + [N II]), F660N ([N II]), and F550M (line-free continuum). These images show an unresolved remnant (FWHM < 0.05'') located within a rich cluster of OB stars which itself is enclosed by a nearly complete interstellar shell seen best in Hα + [N II] emission approximately 8'' × 6'' (150 pc × 110 pc ) in size. The remnant and its associated OB cluster are isolated …
Comparing Various Multi-Component Global Heliosphere Models, H.-R. Müller, V. Florinski, J. Heerikhuisen, V. V. Izmodenov
Comparing Various Multi-Component Global Heliosphere Models, H.-R. Müller, V. Florinski, J. Heerikhuisen, V. V. Izmodenov
Dartmouth Scholarship
Modeling of the global heliosphere seeks to investigate the interaction of the solar wind with the partially ionized local interstellar medium. Models that treat neutr al hydrogen self-consistently and in great detail, together with the plasma, but that neglect magnetic fields, constitute a sub-category within global heliospheric models. There are several different modeling strategies used for this sub-category in the literature. Differences and commonalities in the modeling results from different strategies are pointed out.
A New, Bright, Short-Period, Emission Line Binary In Ophiuchus, M. A. Stark, Richard A. Wade, John R. Thorstensen, Christopher S. Peters
A New, Bright, Short-Period, Emission Line Binary In Ophiuchus, M. A. Stark, Richard A. Wade, John R. Thorstensen, Christopher S. Peters
Dartmouth Scholarship
The 11th magnitude star LS IV-08°3 has been classified previously as an OB star in the Luminous Stars survey, or alternatively as a hot subdwarf. It is actually a binary star. We present spectroscopy, spectroscopic orbital elements, and time-series photometry from observations made at the Kitt Peak National Observatory 2.1 m, Steward Observatory 2.3 m, MDM Observatory 1.3 m and 2.4 m, Hobby-Eberly 9.2 m, and Michigan State University 0.6 m telescopes. The star exhibits emission of varying strength in the cores of H and He I absorption lines. Emission is also present at 4686 Å (He II) and near …
De Canum Venaticorum: A Bright, Eclipsing Red Dwarf–White Dwarf Binary, E. J. M. Van Den Besselaar, R. Greimel, L. Morales-Rueda, G. Nelemans, J. R. Thorstensen
De Canum Venaticorum: A Bright, Eclipsing Red Dwarf–White Dwarf Binary, E. J. M. Van Den Besselaar, R. Greimel, L. Morales-Rueda, G. Nelemans, J. R. Thorstensen
Dartmouth Scholarship
Close white dwarf - red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf - red dwarf binary with a relatively short (~8.7 hours) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters which we discuss in the frame work of common-envelope evolution. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average low-resolution spectrum of …
Optical Imaging And Spectroscopy Of The Galactic Supernova Remnant 3c 58 (G130.7+3.1), Robert Fesen, Gwen Rudie, Alan Hurford, Aljeandro Soto
Optical Imaging And Spectroscopy Of The Galactic Supernova Remnant 3c 58 (G130.7+3.1), Robert Fesen, Gwen Rudie, Alan Hurford, Aljeandro Soto
Dartmouth Scholarship
We present a comprehensive imaging and spectroscopic survey of optical emission knots associated with the young Galactic supernova remnant 3C 58. Hα images show hundreds of clumpy filaments and knots arranged in a complex structure covering a nearly circular area roughly 400'' in diameter. A quite different emission structure is seen in [O III], where the brightest features are less clumpy and largely confined to the remnant's northwest quadrant. Measured radial velocities of over 450 knots reveal two distinct kinematic populations; one with average and peak expansion velocities of 770 and 1100 km s−1, respectively, forming a thick …
The Extinction Toward The Galactic Bulge From Rr Lyrae Stars, Andrea Kunder, Piotr Popowski, Kem H. Cook, Brian Chaboyer
The Extinction Toward The Galactic Bulge From Rr Lyrae Stars, Andrea Kunder, Piotr Popowski, Kem H. Cook, Brian Chaboyer
Dartmouth Scholarship
We present mean reddenings toward 3525 RR0 Lyrae stars from the Galactic bulge fields of the MACHO Survey. These reddenings are determined using the color at minimum V-band light of the RR0 Lyrae stars themselves and are found to be in general agreement with extinction estimates at the same location obtained from other methods. Using 3256 stars located in the Galactic Bulge, we derive the selective extinction coefficient RV,VR = AV/E(V − R) = 4.3 ± 0.2. This value is what is expected for a standard extinction law with R …
The Crab Nebula's Dynamical Age As Measured From Its Northern Filamentary Jet, G. C. Rudie, R. A. Fesen, T. Yamada
The Crab Nebula's Dynamical Age As Measured From Its Northern Filamentary Jet, G. C. Rudie, R. A. Fesen, T. Yamada
Dartmouth Scholarship
We present a deep [O III] 4959,5007 image of the northern filamentary jet in the Crab Nebula taken with the 8.2m Subaru telescope. Using this image and an image taken with the KPNO 4m in 1988 (Fesen & Staker 1993), we have computed proper motions for 35 locations in the jet. The results suggest that when compared to the main body of the remnant, the jet experienced less outward acceleration from the central pulsar's rapidly expanding synchrotron nebula. The jet's apparent expansion rate yields an undecelerated explosion date for the Crab Nebula of 1055 plus or minus 24 C.E., a …
Stellar Population Models And Individual Element Abundances. I. Sensitivity Of Stellar Evolution Models, Aaron Dotter, Brian Chaboyer, Jason W. Ferguson, Hyun-Chul Lee
Stellar Population Models And Individual Element Abundances. I. Sensitivity Of Stellar Evolution Models, Aaron Dotter, Brian Chaboyer, Jason W. Ferguson, Hyun-Chul Lee
Dartmouth Scholarship
Integrated light from distant galaxies is often compared to stellar population models via the equivalent widths of spectral features—spectral indices—whose strengths rely on the abundances of one or more elements. Such comparisons hinge not only on the overall metal abundance, but also on relative abundances. Studies have examined the influence of individual elements on synthetic spectra but little has been done to address similar issues in the stellar evolution models that underlie most stellar population models. Stellar evolution models will primarily be influenced by changes in opacities. In order to explore this issue in detail, 12 sets of stellar evolution …
A High-Resolution Ultraviolet Absorption Spectrum Of Supernova Ejecta In Sn1006, Andrew J. S. Hamilton, Robert A. Fesen, William P. Blair
A High-Resolution Ultraviolet Absorption Spectrum Of Supernova Ejecta In Sn1006, Andrew J. S. Hamilton, Robert A. Fesen, William P. Blair
Dartmouth Scholarship
We report a high-resolution, far-ultraviolet, Space Telescope Imaging Spectrograph (STIS) E140M spectrum of the strong, broad Siii, iii and iv features produced by the ejecta of the supernova of 1006 ad (SN1006) seen in absorption against the background Schweizer–Middleditch OB subdwarf star. The spectrum confirms the extreme sharpness of the red edge of the redshifted Si ii 1260 Å feature, supporting the idea that this edge represents the location of the reverse shock moving into the freely expanding Si-rich ejecta. The expansion velocity of ejecta at the reverse shock is measured to be 7026 ± 3(relative) ±10(absolute) km s−1 …
The Acs Survey Of Galactic Globular Clusters. Ii. Stellar Evolution Tracks, Isochrones, Luminosity Functions, And Synthetic Horizontal-Branch Models, Aaron Dotter, Brian Chaboyer, Darko Jevremović, E. Baron
The Acs Survey Of Galactic Globular Clusters. Ii. Stellar Evolution Tracks, Isochrones, Luminosity Functions, And Synthetic Horizontal-Branch Models, Aaron Dotter, Brian Chaboyer, Darko Jevremović, E. Baron
Dartmouth Scholarship
The ACS Survey of Galactic Globular Clusters, an HST Treasury Project, will deliver high-quality, homogeneous photometry of 65 globular clusters. This paper introduces a new collection of stellar evolution tracks and isochrones suitable for analyzing the ACS survey data. Stellar evolution models were computed at [Fe/H] = -2.5, -2.0, -1.5, -1.0, -0.5, and 0; [α/Fe] = -0.2, 0, 0.2, 0.4, 0.6, and 0.8; and three initial He abundances for masses from 0.1 to 1.8 M⊙ and ages from 2 to 15 Gyr. Each isochrone spans a wide range in luminosity, from MV ~ 14 up to the tip …
The Chemical Distribution In A Subluminous Type Ia Supernova: Hubble Space Telescope Images Of The Sn 1885 Remnant, Robert A. Fesen, Peter A. Hoflich, Andrew J. S. Hamilton, Molly C. Hammell
The Chemical Distribution In A Subluminous Type Ia Supernova: Hubble Space Telescope Images Of The Sn 1885 Remnant, Robert A. Fesen, Peter A. Hoflich, Andrew J. S. Hamilton, Molly C. Hammell
Dartmouth Scholarship
SN 1885 was a probable subluminous SN Ia that occurred in the bulge of the Andromeda galaxy, M31, at a projected location 16'' from the nucleus. Here we present and analyze Hubble Space Telescope images of the SN 1885 remnant seen in absorption against the M31 bulge via the resonance lines of Ca I, Ca II, Fe I, and Fe II. Viewed in Ca II H and K line absorption, the remnant appears as a nearly black circular spot with an outermost angular radius of 0.40'' ± 0.025'', implying a maximum linear radius of 1.52 ± 0.15 pc at M31's …
The Wind‐Ism Interaction Of Α Tauri, Brian E. Wood, Graham M. Harper, Hans-Reinhard Muller, Jacob Heerikhuisen, Gary P. Zank
The Wind‐Ism Interaction Of Α Tauri, Brian E. Wood, Graham M. Harper, Hans-Reinhard Muller, Jacob Heerikhuisen, Gary P. Zank
Dartmouth Scholarship
Ultraviolet spectra of α Tau (K5 III) obtained by the Hubble Space Telescope (HST) show many emission lines affected by broad absorption from the strong wind of this red giant star. For the Mg II h and k lines there is also a narrow absorption feature in the midst of the wind absorption that has been interpreted as being from α Tau's wind-interstellar medium (ISM) interaction region (i.e., its "astrosphere"). We try to reproduce this absorption using hydrodynamic models of the α Tau astrosphere, which show that stellar wind material heated, compressed, and decelerated at the wind's termination …
Discovery Of Extensive Optical Emission Associated With The X-Ray Bright, Radio Faint Galactic Snr G156.2+5.7, Christopher L. Gerardy, Robert A. Fesen
Discovery Of Extensive Optical Emission Associated With The X-Ray Bright, Radio Faint Galactic Snr G156.2+5.7, Christopher L. Gerardy, Robert A. Fesen
Dartmouth Scholarship
We present wide‐field Hα images of the Galactic supernova remnant (SNR) G156.2+5.7 which reveal the presence of considerable faint Hα line emission coincident with the remnant's X‐ray emission. We also present low‐resolution optical spectra for a few representative emission regions. The outermost Hα emission consists largely of long and thin (unresolved), smoothly curved filaments of Balmer‐dominated emission presumably associated with the remnant's forward shock front. Patches of brighter Hα emission along the western, south‐central, and north‐eastern regions appear to be radiative shocked interstellar medium filaments like those commonly seen in SNRs, with relatively strong [O i]λλ6300, 6364 and [S ii]λλ6716, …
Faint X‐Ray Structure In The Crab Pulsar Wind Nebula, F. D. Seward, W. H. Tucker, R. A. Fesen
Faint X‐Ray Structure In The Crab Pulsar Wind Nebula, F. D. Seward, W. H. Tucker, R. A. Fesen
Dartmouth Scholarship
We report on a Chandra observation of the Crab Nebula that gives the first clear view of the faint boundary of the Crab's X-ray-emitting pulsar wind nebula. There is structure in all directions. Fingers, loops, bays, and the south pulsar jet all indicate that either filamentary material or the magnetic field is controlling the relativistic electrons. In general, spectra soften as distance from the pulsar increases but do not change rapidly along linear features. This is particularly true for the pulsar jet. The termination of the jet is abrupt; the east side is close to an [O III] optical filament, …
A Spitzer Space Telescope Study Of Sn 2002hh: An Infrared Echo From A Type Iip Supernova, W. P. S. Meikle, S. Mattila, C. L. Gerardy, R. Kotak, M. Pozzo, S. D. Van Dyk, D. Farrah, R. A. Fesen
A Spitzer Space Telescope Study Of Sn 2002hh: An Infrared Echo From A Type Iip Supernova, W. P. S. Meikle, S. Mattila, C. L. Gerardy, R. Kotak, M. Pozzo, S. D. Van Dyk, D. Farrah, R. A. Fesen
Dartmouth Scholarship
We present late-time (590-994 days) mid-IR photometry of the normal but highly reddened Type IIP supernova SN 2002hh. Bright, cool, slowly fading emission is detected from the direction of the supernova. Most of this flux appears not to be driven by the supernova event but instead probably originates in a cool, obscured star formation region or molecular cloud along the line of sight. We also show, however, that the declining component of the flux is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR emission could also be coming from newly condensed dust and/or an ejecta/CSM impact, …
Heliospheric Response To Different Possible Interstellar Environments, Hans-Reinhard Muller, Priscilla C. Frisch, Vladimir Florinski, Gary P. Zank
Heliospheric Response To Different Possible Interstellar Environments, Hans-Reinhard Muller, Priscilla C. Frisch, Vladimir Florinski, Gary P. Zank
Dartmouth Scholarship
At present, the heliosphere is embedded in a warm, low-density interstellar cloud that belongs to a cloud system flowing through the local standard of rest with a velocity near ~18 km s-1. The velocity structure of the nearest interstellar material (ISM), combined with theoretical models of the local interstellar cloud (LIC), suggest that the Sun passes through cloudlets on timescales of ≤103-104 yr, so the heliosphere has been, and will be, exposed to different interstellar environments over time. By means of a multifluid model that treats plasma and neutral hydrogen self-consistently, the interaction of the …
Grb 060218/Sn 2006aj: A Gamma-Ray Burst And Prompt Supernova Atz= 0.0335, N. Mirabal, J. P. Halpern, D. An, J. R. Thorstensen, D. M. Terndrup
Grb 060218/Sn 2006aj: A Gamma-Ray Burst And Prompt Supernova Atz= 0.0335, N. Mirabal, J. P. Halpern, D. An, J. R. Thorstensen, D. M. Terndrup
Dartmouth Scholarship
We report the imaging and spectroscopic localization of GRB 060218 to a low-metallicity dwarf starburst galaxy at z = 0.03345 ± 0.00006. In addition to making it the second nearest gamma-ray burst known, optical spectroscopy reveals the earliest detection of weak, supernova-like Si II near 5720 Å (~0.1c), starting 1.95 days after the burst trigger. UBVRI photometry obtained between 1 and 26 days postburst confirms the early rise of supernova light, and suggests a short time delay between the gamma-ray burst and the onset of SN 2006aj if the early appearance of a soft component in the X-ray …
Theoretical Uncertainties In Red Giant Branch Evolution: The Red Giant Branch Bump, Stephan R. R. Bjork, Brian Chaboyer
Theoretical Uncertainties In Red Giant Branch Evolution: The Red Giant Branch Bump, Stephan R. R. Bjork, Brian Chaboyer
Dartmouth Scholarship
A Monte Carlo simulation exploring uncertainties in standard stellar evolution theory on the red giant branch of metal-poor globular clusters has been conducted. Confidence limits are derived on the absolute V-band magnitude of the bump in the red giant branch luminosity function (MV,b) and the excess number of stars in the bump, Rb. The analysis takes into account uncertainties in the primordial helium abundance, abundance of α-capture elements, radiative and conductive opacities, nuclear reaction rates, neutrino energy losses, the treatments of diffusion and convection, the surface boundary conditions, and color transformations. The uncertainty in …
From Canonical To Enhanced Extra Mixing In Low‐Mass Red Giants: Tidally Locked Binaries, Pavel A. Denissenkov, Brian Chaboyer, Ke Li
From Canonical To Enhanced Extra Mixing In Low‐Mass Red Giants: Tidally Locked Binaries, Pavel A. Denissenkov, Brian Chaboyer, Ke Li
Dartmouth Scholarship
Stellar models that incorporate simple diffusion or shear-induced mixing are used to describe canonical extra mixing in low-mass red giants of low and solar metallicity. These models are able to simultaneously explain the observed Li and CN abundance changes along the upper red giant branch (RGB) in field low-metallicity stars and match photometry, rotation, and 12C/13C ratios for stars in the old open cluster M67. The shear mixing model requires that main-sequence (MS) progenitors of upper RGB stars possessed rapidly rotating radiative cores and that specific angular momentum was conserved in each of their mass shells during …
The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models For Active And Inactive Solar-Type Stars, Guillermo Torres, Claud H. Lacy, L. A. Marshall, Holly A. Sheets, Jeff A. Mader
The Eclipsing Binary V1061 Cygni: Confronting Stellar Evolution Models For Active And Inactive Solar-Type Stars, Guillermo Torres, Claud H. Lacy, L. A. Marshall, Holly A. Sheets, Jeff A. Mader
Dartmouth Scholarship
We present spectroscopic and photometric observations of the eclipsing system V1061 Cyg (P = 2.35 days). A third star is visible in the spectrum, and the system is a hierarchical triple. We combine the radial velocities for the three stars, times of eclipse, and intermediate astrometric data from the Hipparcos mission (abscissa residuals) to establish the elements of the outer orbit, which is eccentric and has a period of 15.8 yr. We determine accurate values for the masses, radii, and effective temperatures of the binary components: MAa = 1.282 ± 0.015 M☉, RAa = 1.615 …
Near‐Infrared And Optical Limits For The Central X‐Ray Point Source In The Cassiopeia A Supernova Remnant, R. A. Fesen, G. G. Pavlov, D. Sanwal
Near‐Infrared And Optical Limits For The Central X‐Ray Point Source In The Cassiopeia A Supernova Remnant, R. A. Fesen, G. G. Pavlov, D. Sanwal
Dartmouth Scholarship
We set new near-infrared and optical magnitude limits for the central X-ray point source (XPS) in the Cassiopeia A supernova remnant based on HST images. Near-infrared images of the center of Cas A taken with the NICMOS 2 camera in combination with the F110W and F160W filters (~J and H bands) have magnitude limits ≥26.2 and ≥24.6, respectively. These images reveal no sources within a 12 radius (corresponding to a 99% confidence limit) of the Chandra XPS position. The NICMOS data, taken together with broadband optical magnitude limits (R ~ 28 mag) obtained from a deep STIS CCD …
Ubvi Ccd Photometry Of The Old Open Cluster Berkeley 17, Zosia A. C. Krusberg, Brian Chaboyer
Ubvi Ccd Photometry Of The Old Open Cluster Berkeley 17, Zosia A. C. Krusberg, Brian Chaboyer
Dartmouth Scholarship
Photometric UBVI CCD photometry is presented for NGC 188 and Berkeley 17. Color-magnitude diagrams (CMDs) are constructed and reach well past the main-sequence turnoff for both clusters. Cluster ages are determined by means of isochrone fitting to the cluster CMDs. These fits are constrained to agree with spectroscopic metallicity and reddening estimates. Cluster ages are determined to be 7.0 ± 0.5 Gyr for NGC 188 and 10.0 ± 1.0 Gyr for Berkeley 17, where the errors refer to uncertainties in the relative age determinations. These ages are compared to the ages of relatively metal-rich inner halo/thick-disk globular clusters and other …
Hs 2331+3905: The Cataclysmic Variable That Has It All, S. Araujo-Betancor, B. T. Gänsicke, H.-J. Hagen, T. R. Marsh, E T. Harlaftis, J Thorstensen
Hs 2331+3905: The Cataclysmic Variable That Has It All, S. Araujo-Betancor, B. T. Gänsicke, H.-J. Hagen, T. R. Marsh, E T. Harlaftis, J Thorstensen
Dartmouth Scholarship
We report detailed follow-up observations of the cataclysmic variable HS 2331+3905, identified as an emission- line object in the Hamburg Quasar Survey. An orbital period of 81.08 min is unambiguously determined from the detection of eclipses in the light curves of HS 2331+3905. A second photometric period is consistently detected at P ≃ 83.38 min, ∼2.8% longer than Porb, which we tentatively relate to the presence of permanent superhumps. High time resolution photometry exhibits short-timescale variability on time scales of ≃5−6 min which we interpret as non-radial white dwarf pulsations, as well as a coherent signal at 1.12 min, which …
Is First J102347.6+003841 Really A Cataclysmic Binary?, John R. Thorstensen, Eve Armstrong
Is First J102347.6+003841 Really A Cataclysmic Binary?, John R. Thorstensen, Eve Armstrong
Dartmouth Scholarship
The radio source FIRST J102347.6+003841 was presented as the first radio-selected cataclysmic variable star. In the discovery paper, Bond et al. (2002) show a spectrum consistent with a magnetic AM Her–type system, or polar, featuring strong Balmer lines, He I and He II emission lines, and a light curve with rapid, irregular flickering. In contrast, Woudt, Warner, and Pretorius found a smoothly varying light curve with a period near 4.75 hr and one minimum per orbit, indicating that the state of the system had changed dramatically. We present time-resolved spectra showing a superficially normal, mid-G type photosphere, with no detectable …
Probing Multiple Sight Lines Through The Sn 1006 Remnant By Ultraviolet Absorption Spectroscopy, P. Frank Winkler, Knox S. Long, Andrew S. Hamilton, Robert A. Fesen
Probing Multiple Sight Lines Through The Sn 1006 Remnant By Ultraviolet Absorption Spectroscopy, P. Frank Winkler, Knox S. Long, Andrew S. Hamilton, Robert A. Fesen
Dartmouth Scholarship
Absorption-line spectroscopy is an effective probe for cold ejecta within a supernova remnant (SNR), provided that suitable background UV sources can be identified. For the SN 1006 remnant we have identified four such sources, in addition to the much-studied Schweitzer-Middleditch (SM) star. We have used STIS on the Hubble Space Telescope to obtain UV spectra of all four sources, to study "core samples" of the SN 1006 interior. The line of sight closest to the center of the SNR shell, passing only 20 away, is to a V = 19.5 QSO at z = 1.026. Its spectrum shows broad Fe …
Signature Of Electron Capture In Iron‐Rich Ejecta Of Sn 2003du, Peter Hoflich, Christopher L. Gerardy, Ken-Ichi Nomoto, Kentaro Motohara, Robert A. Fesen
Signature Of Electron Capture In Iron‐Rich Ejecta Of Sn 2003du, Peter Hoflich, Christopher L. Gerardy, Ken-Ichi Nomoto, Kentaro Motohara, Robert A. Fesen
Dartmouth Scholarship
Late-time near-infrared and optical spectra of the normal-bright Type Ia supernova 2003du about 300 days after the explosion are presented. At this late epoch, the emission profiles of well-isolated [Fe II] lines (in particular that of the strong 1.644 μm feature) trace out the global kinematic distribution of radioactive material in the expanding supernova ejecta. In SN 2003du, the 1.644 μm [Fe II] line seems to show a flat-topped profile, indicative of a thick but hollow-centered expanding shell, rather than a strongly peaked profile that would be expected from a "center-filled" distribution. Based on detailed models for exploding Chandrasekhar-mass white …
A Million Secondchandraview Of Cassiopeia A, Una Hwang, J. Martin Laming, Carles Badenes, Fred Berendse, John Blondin, Denis Cioffi, Tracey Delaney, Daniel Dewey, Robert Fesen
A Million Secondchandraview Of Cassiopeia A, Una Hwang, J. Martin Laming, Carles Badenes, Fred Berendse, John Blondin, Denis Cioffi, Tracey Delaney, Daniel Dewey, Robert Fesen
Dartmouth Scholarship
We introduce a million second observation of the supernova remnant Cassiopeia A with the Chandra X-Ray Observatory. The bipolar structure of the Si-rich ejecta (northeast jet and southwest counterpart) is clearly evident in the new images, and their chemical similarity is confirmed by their spectra. These are most likely due to jets of ejecta as opposed to cavities in the circumstellar medium, since we can reject simple models for the latter. The properties of these jets and the Fe-rich ejecta will provide clues to the explosion of Cas A.
Location Of The Optical Reverse Shock In The Cassiopeia A Supernova Remnant, Jon A. Morse, Robert A. Fesen, Roger A. Chevalier, Kazimierz J. Borkowski
Location Of The Optical Reverse Shock In The Cassiopeia A Supernova Remnant, Jon A. Morse, Robert A. Fesen, Roger A. Chevalier, Kazimierz J. Borkowski
Dartmouth Scholarship
We use two epochs of Hubble Space Telescope WFPC2 images separated by 2 yr to determine the location and propagation of the reverse shock (RS) in the young supernova remnant Cassiopeia A (Cas A). The images trace optical line emission from fast-moving knots and filaments of highly processed ejecta as they cross the RS, become heated and compressed, and radiatively cool. At numerous positions around the optical shell, new emission features are seen in the 2002 images that were not yet visible in the 2000 exposures. In a few instances emission features seen in the first epoch have completely disappeared …