Publications (47)
The Wind of Variable C in M33
Roberta M. Humphreys, Kris Davidson, Michael Gordon +4
We discuss the spectrum of Var C in M33 obtained just before the onset of its current brightening and recent spectra during its present "eruption" or optically thick wind stage. Th…
Inverted Ionization Zones in Eta Carinae's "Weigelt Knots"
Grant N. Remmen, Kris Davidson, Andrea Mehner
The Weigelt knots, dense slow-moving ejecta near eta Car, are mysterious in structure as well as in origin. Using a special set of spectrograms obtained with the HST/STIS, we have…
The Mass-Loss History of the Red Hypergiant VY CMa
Roberta M. Humphreys, Kris Davidson, A. M. S. Richards +3
Imaging and spectroscopy of the knots, clumps, and extended arcs in the complex ejecta of VY CMa confirm a record of high mass loss events over the past few hundred years. HST/STIS…
Luminous and Variable Stars in M31 and M33. I. The Warm Hypergiants and Post-Red Supergiant Evolution
Roberta M. Humphreys, Kris Davidson, Skyler Grammer +4
The progenitors of Type IIP supernovae have an apparent upper limit to their initial masses of about 20 solar masses, suggesting that the most massive red supergiants evolve to war…
N II 5668-5712, a New Class of Spectral Features in Eta Carinae
Andrea Mehner, Kris Davidson, Gary J. Ferland
We report on the N II 5668-5712 emission and absorption lines in the spectrum of Eta Carinae. Spectral lines of the stellar wind regions can be classified into four physically dist…
Radiation-Driven Stellar Eruptions
Kris Davidson
Very massive stars occasionally expel material in colossal eruptions, driven by continuum radiation pressure rather than blast waves. Some of them rival supernovae in total radiati…
The Unusual Temporal and Spectral Evolution of SN2011ht. II. Peculiar Type IIn or Impostor?
Roberta M. Humphreys, Kris Davidson, Terry J. Jones +5
SN2011ht has been described both as a true supernova and as an impostor. In this paper, we conclude that it does not match some basic expectations for a core-collapse event. We dis…
Where's the Doughnut? LBV bubbles and Aspherical Fast Winds
Adam Frank, Dongsu Ryu, Kris Davidson
In this paper we address the issue of the origin of LBV bipolar bubbles. Previous studies have explained the shapes of LBV nebulae, such as Car, by invoking the interaction of…
The Great Eruption of Eta Carinae
Kris Davidson, Roberta Humphreys
During the years 1838-1858, the very massive star η Carinae became the prototype supernova impostor: it released nearly as much light as a supernova explosion and shed an impressi…
Luminous and Variable Stars in M31 and M33 V. The Upper HR Diagram
Roberta M. Humphreys, Kris Davidson, David Hahn +2
We present HR Diagrams for the massive star populations in M31 and M33 including several different types of emission-line stars: the confirmed Luminous Blue Variables (LBVs), candi…
Crossing the `Yellow Void' -- Spatially Resolved Spectroscopy of the Post- Red Supergiant IRC+10420 and Its Circumstellar Ejecta
Roberta M. Humphreys, Kris Davidson, Nathan Smith
IRC +10420 is one of the extreme hypergiant stars that define the empirical upper luminosity boundary in the HR diagram. During their post--RSG evolution, these massive stars enter…
Eta Carinae's Declining Outflow Seen in the UV, 2002-2015
Kris Davidson, Kazunori Ishibashi, John C. Martin +1
Existing HST UV data offer many previously neglected clues to eta Car's behavior since 2000. Here we examine a subset of observations with diverse results. (1) The star's rapid cha…
A Sea Change in Eta Carinae
Andrea Mehner, Kris Davidson, Roberta M. Humphreys +4
Major stellar-wind emission features in the spectrum of Eta Car have recently decreased by factors of order 2 relative to the continuum. This is unprecedented in the modern observa…
X-ray Spectral Variation of Eta Carinae through the 2003 X-ray Minimum
Kenji Hamaguchi, Michael F. Corcoran, Theodore Gull +7
We report the results of an X-ray observing campaign on the massive, evolved star Eta Carinae, concentrating on the 2003 X-ray minimum as seen by the XMM-Newton observatory. These…
The Morphology of IRC +10420's Circumstellar Ejecta
Chelsea Tiffany, Roberta M. Humphreys, Terry J. Jones +1
Images of the circumstellar ejecta associated with the post-red supergiant IRC +10420 show a complex ejecta with visual evidence for episodic mass loss. In this paper we describe t…
Latitude-dependent effects in the stellar wind of Eta Carinae
Nathan Smith, Kris Davidson, Theodore R. Gull +2
The Homunculus reflection nebula around eta Carinae provides a rare opportunity to observe the spectrum of a star from multiple latitudes. We present STIS spectra of several positi…
The Photometric and Spectral Evolution of the 2008 Luminous Optical Transient in NGC 300
Roberta M. Humphreys, Howard E. Bond, Alceste Z. Bonanos +4
The 2008 optical transient in NGC 300 is one of a growing class of intermediate-luminosity transients that brighten several orders of magnitude from a previously optically obscured…
The Early Spectra of Eta Carinae 1892 to 1941 and the Onset of Its High Excitation Emission Spectrum
Roberta M. Humphreys, Kris Davidson, Michael Koppleman
The observed behavior of eta Car from 1860 to 1940 has not been considered in most recent accounts, nor has it been explained in any quantitative model. We have used modern digital…
Penetrating the Homunculus -- Near-Infrared Adaptive Optics Images of Eta Carinae
Ãtienne Artigau, John C. Martin, Roberta M. Humphreys +3
Near-infrared adaptive optics imaging with NICI and NaCO reveal what appears to be a three-winged or lobed pattern, the "butterfly nebula", outlined by bright Br and H em…
Mid-Cycle Changes in Eta Carinae
John C. Martin, Kris Davidson, Roberta M. Humphreys +1
In late 2006, ground-based photometry of Car plus the Homunculus showed an unexpected decrease in its integrated apparent brightness, an apparent reversal of its long-term bri…
On the Spatial Distribution of Luminous Blue Variables, B[e] Supergiants, and Wolf-Rayet stars in the Large Magellanic Cloud
John C. Martin, Roberta M. Humphreys, Kris Davidson
We examine the spatial distributions of LBVs, B[e] supergiants, and W-R stars in the LMC, to clarify their relative ages, evolutionary states, and relationships. This survey employ…
Critical Differences and Clues in Eta Car's 2009 Event
Andrea Mehner, Kris Davidson, John C. Martin +3
We monitored Eta Carinae with HST WFPC2 and Gemini GMOS throughout the 2009 spectroscopic event, which was expected to differ from its predecessor in 2003 (Davidson et al. 2005). H…
A spectral and spatial analysis of eta Carinae's diffuse X-ray emission using CHANDRA
Kerstin Weis, Michael F. Corcoran, Dominik J. Bomans +1
The luminous unstable star (star system) eta Carinae is surrounded by an optically bright bipolar nebula, the Homunculus and a fainter but much larger nebula, the so-called outer e…
A spectroscopic event of eta Car viewed from different directions: The data and first results
Otmar Stahl, Kerstin Weis, Dominik J. Bomans +3
We present spectroscopic observations with high spectral resolution of eta Car as seen by the SE lobe of the Homunculus nebula over the 2003.5 "spectroscopic event". The observed s…
High-excitation emission lines near eta Carinae, and its likely companion star
Andrea Mehner, Kris Davidson, Gary J. Ferland +1
In order to study the distribution of gas and ionizing radiation around eta Car and their implications for its likely companion star, we have examined high-excitation emission line…
The Hidden Clumps in VY CMa Uncovered by ALMA
Roberta M. Humphreys, A. M. S. Richards, Kris Davidson +3
The red hypergiant VY CMa is famous for its very visible record of high mass loss events. Recent CO observations with ALMA revealed three previously unknown large scale outflows (P…
Eta Carinae's 2014.6 Spectroscopic Event: The Extraordinary He II and N II Features
Kris Davidson, Andrea Mehner, Roberta Humphreys +2
Eta Carinae's spectroscopic events (periastron passages) in 2003, 2009, and 2014 differed progressively. He II 4687 and nearby N II multiplet 5 have special significance because th…
A High-Resolution Study of Eta Carinae's Outer Ejecta
Kerstin Weis, Michael F. Corcoran, Kris Davidson +1
Eta Carinae is a very luminous and unstable evolved star. Outflowing material ejected during the star's giant eruption in 1843 surrounds it as a nebula which consists of an inner b…
Spitzer Space Telescope Infrared Imaging and Spectroscopy of the Crab Nebula
Tea Temim, Robert D. Gehrz, Charles E. Woodward +7
We present 3.6, 4.5, 5.8, 8.0, 24, and 70 micron images of the Crab Nebula obtained with the Spitzer Space Telescope IRAC and MIPS cameras, Low- and High-resolution Spitzer IRS spe…
On the X-ray emission of Eta Carinae's outer ejecta
Kerstin Weis, Michael F. Corcoran, Kris Davidson
The extremely luminous and unstable star Eta Carinae is surrounded by ejecta formed during the star's giant eruption around 1843. The optical nebula consists of an inner region, th…
Luminous and Variable Stars in NGC 2403 and M81
Roberta M. Humphreys, Sarah Stangl, Michael S. Gordon +2
We present the results of spectroscopy and multi-wavelength photometry of luminous and variable star candidates in the nearby spiral galaxies NGC 2403 and M81. We discuss specific…
Physical conditions in the Homunculus
Gary J. Ferland, Nick Abel, Kris Davidson +1
Conditions within the Homunculus nebula around Eta Car are determined by many of the same physical processes that occur in molecular clouds in the interstellar medium. But there is…
Recovery from Giant Eruptions in Very Massive Stars
Amit Kashi, Kris Davidson, Roberta M. Humphreys
We use a hydro-and-radiative-transfer code to explore the behavior of a very massive star (VMS) after a giant eruption -- i.e., following a supernova impostor event. Beginning with…
High Resolution, Long - Slit Spectroscopy of VY CMa: The Evidence for Localized High Mass Loss Events
Roberta M. Humphreys, Kris Davidson, Gerald Ruch +1
High spatial and spectral resolution spectroscopy of the OH/IR supergiant VY CMa and its circumstellar ejecta reveals evidence for high mass loss events from localized regions on t…
Speckle-masking imaging polarimetry of Eta Carinae: evidence for an equatorial disk
Heino Falcke, Kris Davidson, Karl-Heinz Hofmann +1
With our new speckle imaging polarimeter we have obtained first polarimetric images with sub-arcsecond resolution of the Luminous Blue Variable eta Carinae in the Halpha line. The…
On the Social Traits of Luminous Blue Variables
Roberta M. Humphreys, Kerstin Weis, Kris Davidson +1
In a recent paper, Smith and Tombleson (2015) state that the Luminous Blue Variables (LBVs) in the Milky Way and the Magellanic Clouds are isolated; that they are not spatially ass…
The Infrared-Bright SW Knots in the Complex Ejecta of VY CMa
Roberta M. Humphreys, Terry J. Jones, Kris Davidson +4
The red hypergiant VY CMa is remarkable for its very visible record of high mass loss events observed over the range of wavelengths from the optical and infrared to the submillimet…
Luminous and Variable Stars in M31 and M33. II. Luminous Blue Variables, Candidate LBVs, Fe II Emission Line Stars, and Other Supergiants
Roberta M. Humphreys, Kerstin Weis, Kris Davidson +2
An increasing number of non-terminal eruptions are being found in the numerous surveys for optical transients. Very little is known about these giant eruptions, their progenitors a…
VLT-UVES observations of the Balmer line variations of eta Carinae during the 2003 spectroscopic event
Kerstin Weis, Otmar Stahl, Dominik J. Bomans +3
We present high spectral resolution echelle observations of the Balmer line variations during the 2003.5 ``spectroscopic event'' of eta Carinae. Spectra have been recorded of both…
Mapping the Asymmetric Thick Disk: III. The Kinematics and Interaction with the Galactic Bar
Roberta M. Humphreys, Timothy C. Beers, Juan E. Cabanela +4
In the first two papers of this series, Larsen et al (2010a,b) describe our faint CCD survey in the inner Galaxy and map the over-density of Thick Disk stars in Quadrant I (Q1) to…
The Chrysalis Opens? Photometry from the Eta Carinae HST Treasury Project, 2002-2006
J. C. Martin, Kris Davidson, M. D. Koppelman
During the past decade Eta Car has brightened markedly, possibly indicating a change of state. Here we summarize photometry gathered by the Hubble Space Telescope as part of the HS…
Gaia, Trumpler 16, and Eta Carinae
Kris Davidson, Greta Helmel, Roberta M. Humphreys
Gaia parallaxes for the star cluster Tr 16 reveal a discrepancy in the oft-quoted distance of Eta Carinae. It is probably more distant and more luminous. Moreover, many presumed me…
LBVs and Statistical Inference
Kris Davidson, Roberta M. Humphreys, Kerstin Weis
Smith and Tombleson (2015) asserted that statistical tests disprove the standard view of LBVs, and proposed a far more complex scenario to replace it. But Humphreys et al. (2016) s…
The Altered State of Carinae: HST's Photometric Record 1998--2021
John C. Martin, Kris Davidson, Roberta M. Humphreys +1
Hubble Space Telescope photometry of Carinae spans 23 years, including five spectroscopic events. The rapid brightening rate decreased after 2010, and the spectroscopic events…
Giant eruptions of very massive stars
Kris Davidson
Giant eruptions or supernova-impostor events are far more mysterious than true supernovae. An extreme example can release as much radiative energy as a SN, ejecting several M_sun o…
Secular Changes in Eta Carinae's Wind 1998-2011
Andrea Mehner, Kris Davidson, Roberta M. Humphreys +4
Stellar wind-emission features in the spectrum of eta Carinae have decreased by factors of 1.5-3 relative to the continuum within the last 10 years. We investigate a large data set…
A Tale of Two Impostors: SN2002kg and SN1954J in NGC 2403
Roberta M. Humphreys, Kris Davidson, Schuyler D. Van Dyk +1
We describe new results on two supernova impostors in NGC 2403, SN 1954J(V12) and SN 2002kg(V37). For the famous object SN 1954J we combine four critical observations: its current…