Physical Sciences and Mathematics Commons^™

Two Substellar Survivor Candidates; One Found And One Missing, T. Von Hippel, N. Walters, J. Farihi, T.R. Marsh, E. Breedt, P.W. Cauley, J.J. Hermes

Publications

This study presents observations of two possible substellar survivors of post-main sequence engulfment, currently orbiting white dwarf stars. Infrared and optical spectroscopy of GD 1400 reveal a 9.98 h orbital period, where the benchmark brown dwarf has 𝑀2 = 68 ± 8 MJup, 𝑇eff ≈ 2100 K, and a cooling age under 1 Gyr. A substellar mass in the lower range of allowed values is favoured by the gravitational redshift of the primary. Synthetic brown dwarf spectra are able to reproduce the observed CO bands, but lines below the bandhead are notably overpredicted. The known infrared excess towards PG 0010+281 …

Collisions In A Gas-Rich White Dwarf Planetary Debris Disc, Ted Von Hippel, University College London, Scott J. Kenyon, Jay Farihi, Erik Dennihy, Boris T. Gänsicke, J.J. Hermes, Carl Melis

Publications

WD 0145+234 is a white dwarf that is accreting metals from a circumstellar disc of planetary material. It has exhibited a substantial and sustained increase in 3–5 μm flux since 2018. Follow-up Spitzer photometry reveals that emission from the disc had begun to decrease by late 2019. Stochastic brightening events superimposed on the decline in brightness suggest the liberation of dust during collisional evolution of the circumstellar solids. A simple model is used to show that the observations are indeed consistent with ongoing collisions. Rare emission lines from circumstellar gas have been detected at this system, supporting the emerging picture …

Near-Infrared Variability In Dusty White Dwarfs: Tracing The Accretion Of Planetary Material, Laura K. Rogers, Siyi Xu, Amy Bonsor, Simon Hodgkin, Kate Y.L. Su, Ted Von Hippel, Michael Jura

Publications

The inwards scattering of planetesimals towards white dwarfs is expected to be a stochastic process with variability on human time-scales. The planetesimals tidally disrupt at the Roche radius, producing dusty debris detectable as excess infrared emission. When sufficiently close to the white dwarf, this debris sublimates and accretes on to the white dwarf and pollutes its atmosphere. Studying this infrared emission around polluted white dwarfs can reveal how this planetary material arrives in their atmospheres. We report a near-infrared monitoring campaign of 34 white dwarfs with infrared excesses with the aim to search for variability in the dust emission. Time …

Polarization Measurements Of The Polluted White Dwarf G29-38, Ted Von Hippel, Daniel V. Cotton, Jeremy Bailey, J.E. Pringle, William B. Sparks, Jonathan P. Marshall

Publications

We have made high-precision polarimetric observations of the polluted white dwarf G29-38 with the HIgh Precision Polarimetric Instrument 2. The observations were made at two different observatories – using the 8.1-m Gemini North Telescope and the 3.9-m Anglo-Australian Telescope – and are consistent with each other. After allowing for a small amount of interstellar polarization, the intrinsic linear polarization of the system is found to be 275.3 ± 31.9 parts per million at a position angle of 90.8 ± 3.8◦ in the SDSS g

band. We compare the observed polarization with the predictions of circumstellar disc models. The measured polarization …

Magnetospherically-Trapped Dust And A Possible Model For The Unusual Transits At Wd1145+017, J. Farihi, Ted Von Hippel, J. E. Pringle

Ted von Hippel

The rapidly evolving dust and gas extinction observed towardsWD1145+017 has opened a real-time window onto the mechanisms for destruction-accretion of planetary bodies onto white dwarf stars, and has served to underline the importance of considering the dynamics of dust particles around such objects. Here it is argued that the interaction between (charged) dust grains and the stellar magnetic field is an important ingredient in understanding the physical distribution of infrared emitting particles in the vicinity of such white dwarfs. These ideas are used to suggest a possible model for WD 1145+017 in which the unusual transit shapes are caused by …

Dust Production And Depletion In Evolved Planetary Systems, J. Farihi, Ted Von Hippel, Rik Van Lieshout, P.W. Cauley, Erik Dennihy, Et Al.

Ted von Hippel

The infrared dust emission from the white dwarf GD 56 is found to rise and fall by 20 per cent peak-to-peak over 11.2 yr, and is consistent with ongoing dust production and depletion. It is hypothesized that the dust is produced via collisions associated with an evolving dust disc, temporarily increasing the emitting surface of warm debris, and is subsequently destroyed or assimilated within a few years. The variations are consistent with debris that does not change temperature, indicating that dust is produced and depleted within a fixed range of orbital radii. Gas produced in collisions may rapidly re-condense onto …

Dust Production And Depletion In Evolved Planetary Systems, J. Farihi, Ted Von Hippel, Rik Van Lieshout, P.W. Cauley, Erik Dennihy, Et Al.

Publications

The infrared dust emission from the white dwarf GD 56 is found to rise and fall by 20 per cent peak-to-peak over 11.2 yr, and is consistent with ongoing dust production and depletion. It is hypothesized that the dust is produced via collisions associated with an evolving dust disc, temporarily increasing the emitting surface of warm debris, and is subsequently destroyed or assimilated within a few years. The variations are consistent with debris that does not change temperature, indicating that dust is produced and depleted within a fixed range of orbital radii. Gas produced in collisions may rapidly re-condense onto …

Revealing The Structure Of The Outer Disks Of Be Stars, Robert Klement, Anthony C. Carciofi, Thomas Rivinius, Lynn D. Matthews, Rodrigo G. Vieira, Richard Ignace, Jon E. Bjorkman, B. C. Mota, Daniel M. Faes, A. D. Bratcher, M. Cure, Stanislav Stefl

Richard Ignace

Context. The structure of the inner parts of Be star disks (≲ 20 stellar radii) is well explained by the viscous decretion disk (VDD) model, which is able to reproduce the observable properties of most of the objects studied so far. The outer parts, on the other hand, are not observationally well-explored, as they are observable only at radio wavelengths. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for several Be stars that were previously detected in the radio, but a convincing physical explanation for this trend has not yet been provided.

Aims. We …

Magnetospherically-Trapped Dust And A Possible Model For The Unusual Transits At Wd1145+017, J. Farihi, Ted Von Hippel, J. E. Pringle

Publications

The rapidly evolving dust and gas extinction observed towardsWD1145+017 has opened a real-time window onto the mechanisms for destruction-accretion of planetary bodies onto white dwarf stars, and has served to underline the importance of considering the dynamics of dust particles around such objects. Here it is argued that the interaction between (charged) dust grains and the stellar magnetic field is an important ingredient in understanding the physical distribution of infrared emitting particles in the vicinity of such white dwarfs. These ideas are used to suggest a possible model for WD 1145+017 in which the unusual transit shapes are caused by …

Revealing The Structure Of The Outer Disks Of Be Stars, Robert Klement, Anthony C. Carciofi, Thomas Rivinius, Lynn D. Matthews, Rodrigo G. Vieira, Richard Ignace, Jon E. Bjorkman, B. C. Mota, Daniel M. Faes, A. D. Bratcher, M. Cure, Stanislav Stefl

ETSU Faculty Works

Context. The structure of the inner parts of Be star disks (≲ 20 stellar radii) is well explained by the viscous decretion disk (VDD) model, which is able to reproduce the observable properties of most of the objects studied so far. The outer parts, on the other hand, are not observationally well-explored, as they are observable only at radio wavelengths. A steepening of the spectral slope somewhere between infrared and radio wavelengths was reported for several Be stars that were previously detected in the radio, but a convincing physical explanation for this trend has not yet been provided.

Aims. We …

Evidence Of A Mira-Like Tail And Bow Shock About The Semi-Regular Variable V Cvn From Four Decades Of Polarization Measurements., Hilding Neilson, Richard Ignace, Beverly Smith, Gary Henson, Alyssa Adams

ETSU Faculty Works

Polarization is a powerful tool for understanding stellar atmospheres and circumstellar environments. Mira and semi-regular variable stars have been observed for decades and some are known to be polarimetrically variable, however, the semi-regular variable V Canes Venatici displays an unusually large, unexplained amount of polarization. We present ten years of optical polarization observations obtained with the HPOL instrument, supplemented by published observations spanning a total interval of about forty years for V CVn. We find that V CVn shows large polarization variations ranging from 1 - 6%. We also find that for the past forty years the position angle measured …

Evidence Of A Mira-Like Tail And Bow Shock About The Semi-Regular Variable V Cvn From Four Decades Of Polarization Measurements., Hilding R. Neilson, Richard Ignace, Beverly J. Smith, Gary Henson, Alyssa M. Adams

Richard Ignace

The Continuum Linear Polarization Signature Of Classical Be Stars, Robbie J. Halonen

Electronic Thesis and Dissertation Repository

Classical Be stars are rapidly-rotating, massive stars that exhibit distinct observational characteristics due to the presence of enveloping, equatorial disks of gas. While diligent observation of these objects has established a reliable description of their geometric and kinematic properties, our understanding of classical Be stars remains distressingly limited on the dynamical front. Principally, we lack a satisfactory characterization of the physical process(es) through which the gaseous disks form and dissipate. In order to understand the mechanisms that govern the development of these enigmatic stars, we use computational codes to produce theoretical models of these objects and their environments. We compare …

Using Photometry To Probe The Circumstellar Environment Of Δ Scorpii, Carol E. Jones, Paul A. Wiegert, Christopher Tycner, Gregory W. Henry, Richard P. Cyr, Robbie J. Halonen, Matthew W. Muterspaugh

Information Systems and Engineering Management Research Publications

We acquired Johnson BV photometry of the binary Be disk system δ Scorpii during its 2009, 2010, 2011, and 2012 observing seasons and used it to probe the innermost regions of the disk. We found that several disk building events have occurred during this time, resulting in an overall brightening in the V band and reddening of the system. In addition to these long-term trends, we found cyclical variability in each observing season on timescales between 60 and 100 days. We were able to reproduce the changes in the magnitude and color of δ Sco using our theoretical models and …

Rotational And Cyclical Variability In Γ Cassiopeiae. Ii. Fifteen Seasons, Gregory W. Henry, Myron A. Smith

Information Systems and Engineering Management Research Publications

The B0.5 IVe star γ Cas is of great interest because it is the prototype of a small group of classical Be stars having hard X-ray emission of unknown origin. We discuss results from ongoing B and V observations of the γ Cas star–disk system acquired with an Automated Photometric Telescope during the observing seasons 1997–2011. In an earlier study, Smith, Henry, & Vishniac showed that light variations in γ Cas are dominated by a series of comparatively prominent cycles with amplitudes of 0.02–0.03 mag and lengths of 2–3 months, superimposed on a 1.21 day periodic signal some five times …

The Relationship Between Γ Cassiopeiae’S X-Ray Emission And Its Circumstellar Environment Ii. Geometry And Kinematics Of The Disk From Mirc And Vega Instruments On The Chara Array, Philippe Stee, O. Delaa, John D. Monnier, Anthony Meilland, Karine Perraut, Denis Mourard, Xiao Che, Gail H. Schaefer, Ettore Pedretti, Myron A. Smith, Raimundo Lopes De Oliveira, Christian Motch, Gregory W. Henry, Noel D. Richardson, Karen S. Bjorkman, R. Bücke, E. Pollmann, Juan Zorec, Douglas R. Gies, Theo A. Ten Brummelaar, Harold A. Mcalister, Nils H. Turner, Judit Sturmann, Laszlo Sturmann, Stephen T. Ridgway

Information Systems and Engineering Management Research Publications

Context.γ Cas is thought to be the prototype of classical Be stars and is the most studied object among this group. However, as for all Be stars, the origin and the physics of its circumstellar disk responsible for the observed near IR-excess, emission lines, and peculiar X-ray emission is still being debated.

Aims. We constrain the geometry and kinematics of its circumstellar disk from the highest spatial resolution ever achieved on this star. This investigation is a part of a large multi-technique observing campaign to obtain the most complete picture of γ Cas which emphasizes the relation of the …

The Relationship Between Γ Cassiopeiae’S X-Ray Emission And Its Circumstellar Environment, Myron A. Smith, Raimundo Lopes De Oliveira, Christian Motch, Gregory W. Henry, Noel D. Richardson, Karen S. Bjorkman, Philippe Stee, Denis Mourard, John D. Monnier, Xiao Che, R. Bücke, E. Pollmann, Douglas R. Gies, Gail Schaefer, Theo A. Ten Brummelaar, Harold Mcalister, Nils H. Turner, Judit Sturmann, Laszlo Sturmann, Stephen T. Ridgway

Information Systems and Engineering Management Research Publications

γ Cas is the prototypical classical Be star and is recently best known for its variable hard X-ray emission. To elucidate the reasons for this emission, we mounted a multiwavelength campaign in 2010 centered around four XMM-Newton observations. The observational techniques included long baseline optical interferometry (LBOI) from two instruments at CHARA, photometry carried out by an automated photometric telescope and Hα observations. Because γ Cas is also known to be in a binary, we measured radial velocities from the Hα line and redetermined its period as 203.55 ± 0.20 days and its eccentricity as near zero. The LBOI observations …

Dust And The Type Ii-Plateau Supernova 2004dj, W. P. S. Meikle, R. Kotak, D. Farrah, S. Mattila, S. D. Van Dyk, A. C. Andersen, R. Fesen

Dartmouth Scholarship

We present mid-infrared (MIR) spectroscopy of a Type II-plateau supernova, SN 2004dj, obtained with the Spitzer Space Telescope, spanning 106-1393 days after explosion. MIR photometry plus optical/near-IR observations are also reported. An early-time MIR excess is attributed to emission from non-silicate dust formed within a cool dense shell (CDS). Most of the CDS dust condensed between 50 days and 165 days, reaching a mass of 0.3 × 10^–5 M _☉. Throughout the observations, much of the longer wavelength (>10 μm) part of the continuum is explained as an IR echo from interstellar dust. The MIR excess …

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 …

The New Class Of Dusty Daz White Dwarfs, Ted Von Hippel, Et Al.

Publications

Our mid-infrared survey of 124 white dwarfs with the Spitzer Space Telescope and the IRAC imager has revealed an infrared excess associated with the white dwarf WD 2115-560 naturally explained by circumstellar dust. This object is the fourth white dwarf observed to have circumstellar dust. All four are DAZ white dwarfs, i.e., they have both photospheric Balmer lines and photospheric metal lines. We discuss these four objects as a class, which we abbreviate "DAZd," where the "d" stands for "dust." Using an optically thick, geometrically thin disk model analogous to Saturn's rings, we find that the inner disk edges are …

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 …

Spectroscopy Of Early F Stars: Γ Doradus Candidates And Possible Metallic Shell Stars, Francis C. Fekel, Phillip B. Warner, Anthony B. Kaye

Information Systems and Engineering Management Research Publications

We obtained high-resolution spectroscopic observations of 34 γ Doradus candidates. From the red-wavelength spectra, we determined spectral classes, radial velocities, and projected rotational velocities. The spectra of seven late A or early F stars show metallic lines that have composite profiles consisting of a narrow component near the center of a broad line, indicating that they may be shell stars or binaries. Several stars, including HD 152896, HD 173977, HD 175337, and HD 195068/9, show large line profile asymmetries. Two stars, HD 11443 (=α Trianguli) and HD 149420, are ellipsoidal variables and not γ Doradus stars. The percentage of binary …

X-Ray And Optical Variations In The Classical Be Star Γ Cassiopeia: The Discovery Of A Possible Magnetic Dynamo, Richard D. Robinson, Myron A. Smith, Gregory W. Henry

Information Systems and Engineering Management Research Publications

The classical B0.5e star γ Cassiopeia is known to be a unique X-ray source by virtue of its moderate LX (1033 ergs s-1), hard X-ray spectrum, and light curve punctuated by ubiquitous flares and slow undulations. The peculiarities of this star have led to a controversy concerning the origin of these emissions: whether they are from wind infall onto a putative degenerate companion, as in the case of normal Be/X-ray binaries, or from the Be star itself. Recently, much progress has been made to resolve this question: (1) the discovery that γ Cas is a moderately eccentric binary system (P …

Mid-Infrared Visibility Measurements Of Evolved Stars, Jeffrey J. Sudol, H. M. Dyck, R. E. Stencel, D. I. Klebe, M. J. Creech-Eakman

Physics & Engineering Faculty Publications

No abstract provided.

Optical Variability In The Unusual K5 V Infrared-Excess Star Hd 98800, Gregory W. Henry, Douglas S. Hall

Information Systems and Engineering Management Research Publications

The dusty infrared-excess star HD 98800 (K5 V) was observed for several weeks in the spring of 1993 by the Vanderbilt/Tennessee State 0.4 m automatic photoelectric telescope. It was found to be a variable star with an amplitude of 0.07 mag in V and a period of 14.7 days. We show, by comparison with other chromospherically active variable stars and constant stars with good observational histories, that the Rossby number for HD 98800, determined to be 0.30, places it well within the regime of stars whose convective envelopes and rotation rates combine to drive a magnetic dynamo strong enough to …

Evidence Signalling The Start Of Enhanced Counterjet Flow In The Symbiotic System R Aquarii, A. G. Michalitsianos, M. Perez, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

The velocity structure of strong far-UV emission lines observed in the symbiotic variable R Aqr suggests the start of new jet activity which will probably culminate in the appearance of a series of intense nebular emission knots within a decade. This is indicated by a systematic redward wavelength drift of emission lines, which we have followed with the International Ultraviolet Explorer (IV E) since the discovery of the brilliant northeast jet emission knots more than 10 years ago. The C IV λλ1548, 1550 resonance lines, which previously showed a prominent blue asymmetric wing that extended to velocities in excess -200 …

Optical Spectroscopy Of The Dusty K5 V Star Hd 98800, Francis C. Fekel, Bernard W. Bopp

Information Systems and Engineering Management Research Publications

High-resolution CCD spectra of the red region of the dusty K5 V star HD 98800, which may contain a protoplanetary disk, have been obtained at Kitt Peak National Observatory. The spectra verify the dwarf spectral type and show rotationally broadened photospheric lines, Hα emission, and a very strong Li _Ι λ6707 absorption line, all of which confirm the star as a very young object. The overall spectrum of HD 98800 closely resembles that of the young, chromospherically active, single BY Dra star HD 82558 (=LQ Hya). The measured Li _Ι equivalent width of 0.39 Å implies an abundance log N …