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Carpenter, Kenneth G.

Publications and source records attributed to Carpenter, Kenneth G..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

The Advanced Spectral Library (ASTRAL): Reference Spectra for Evolved M Stars

The HST Treasury Program Advanced Spectral Library Project: Cool Stars was designed to collect representative, high-quality UV spectra of eight evolved FM type cool stars. The Space Telescope Imaging Spectrograph (STIS)echelle spectra of these objects enable investigations of a broad range of topics, including stellar and interstellar astrophysics. This paper provides a guide to the spectra of the two evolved M stars, the M2 Iab supergiant Oriand the M3.4 giant Cru, with comparisons to the prototypical K1.5 giant Boo. It includes identifications of the significant atomic and molecular emission and absorption features and discusses the character of the photospheric and chromospheric continua and line spectra. The fluorescent processes responsible for a large portion of the emission-line spectrum, the characteristics of the stellar winds, and the available diagnostics for hot and cool plasmas are also summarized. This analysis will facilitate the future study of the spectra, outer atmospheres, and winds, not only of these objects but of numerous other cool, low-gravity stars, for years to come.

The HST Treasury Program Advanced Spectral Library↗
NASA NTRS2018

The Advanced Spectral Library (ASTRAL): Reference Spectra for Evolved M Stars

The HST (Hubble Space Telescope) Treasury Program Advanced Spectral Library Project: Cool Stars was designed to collect representative, high-quality ultraviolet spectra of eight evolved F-M type cool stars. The Space Telescope Imaging Spectrograph (STIS) echelle spectra of these objects enable investigations of a broad range of topics, including stellar and interstellar astrophysics. This paper provides a guide to the spectra of the two evolved M stars, the M2 Iab super giant alpha Ori and the M3.4 giant gamma Cru, with comparisons to the prototypical K1.5 giant alpha Boo. It includes identifications of the significant atomic and molecular emission and absorption features and discusses the character of the photospheric and chromospheric continua and line spectra. The fluorescent processes responsible for a large portion of the emission-line spectrum, the characteristics of the stellar winds, and the available diagnostics for hot and cool plasmas are also summarized. This analysis will facilitate the future study of the spectra, outer atmospheres, and winds, not only of these objects but of numerous other cool, low-gravity stars, for years to come.

M Stars↗
NASA NTRS2018

HST/GHRS Observations of Cool, Low-Gravity Stars. VI. Mass-Loss Rates and Wind Parameters for M Giants

The photon-scattering winds of M giants absorb parts of the chromospheric emission lines and produce self-reversed spectral features in high-resolution Hubble Space Telescope (HST)/GHRS spectra. These spectra provide an opportunity to assess fundamental parameters of the wind, including flow and turbulent velocities, the optical depth of the wind above the region of photon creation, and the star’s mass-loss rate. This paper is the last paper in the series “GHRS Observations of Cool, Low-Gravity Stars”; the last several have compared empirical measurements of spectral emission lines with models of the winds and mass loss of K giants and supergiants. We have used the Sobolev with Exact Integration radiative transfer code, along with simple models of the outer atmosphere and wind, to determine and compare the wind characteristics of the two M-giant stars, gamma Cru (M3.5III) and mu Gem (M3IIIab), with previously derived values for low-gravity K-stars. The analysis specifies the wind parameters and calculates line profiles for the Mg II resonance lines, in addition to a range of unblended Fe II lines. Our line sample covers a large range of wind opacities and, therefore, probes a range of heights in the atmosphere. Our results show that mu Gem has a slower and more turbulent wind than gamma Cru. Also, mu Gem has a weaker chromosphere, in terms of surface flux, with respect to gamma Cru. This suggests that mu Gem is more evolved than gamma Cru. Comparing the two M giants in this work with previously studied K-giant and supergiant stars (alpha Tau, gamma Dra, and lambda Vel) reveals that the M giants have slower winds than the earlier giants, but exhibit higher mass-loss rates. Our results are interpreted in the context of the winds being driven by Alfvén waves.

chromospheric emission lines↗
NASA NTRS2018

The Mass of the Cepheid V350 Sgr

V350 Sgr is a classical Cepheid suitable for mass determination. It has a hot companion which is prominent in the ultraviolet (UV) and which is not itself a binary. We have obtained two high-resolution echelle spectra of the companion at orbital velocity maximum and minimum with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope in the 1320 to 1510 Å region. By cross-correlating these spectra we obtained the orbital velocity amplitude of the companion with an uncertainty in the companion amplitude of 1.9 km s(exp −1). This provides a mass ratio of the Cepheid to the companion of 2.1. The UV energy distribution of the companion provides the mass of the companion, yielding a Cepheid mass of 5.2 ± 0.3 solar mass. This mass requires some combination of moderate main sequence core convective overshoot and rotation to match evolutionary tracks.

V350 Sgr↗
DOE OSTI2016

Lithium in open cluster red giants hosting substellar companions

We have measured stellar parameters, [Fe/H], lithium abundances, rotation, and {sup 12}C/{sup 13}C in a small sample of red giants (RGs) in three open clusters that are each home to a RG star that hosts a substellar companion (SSC) (NGC 2423 3, NGC 4349 127, and BD+12 1917 in M67). Our goal is to explore whether the presence of SSCs influences the Li content. Both {sup 12}C/{sup 13}C and stellar rotation are measured as additional tracers of stellar mixing. One of the companion hosts, NGC 2423 3, is found to be Li-rich with A(Li){sub NLTE} = 1.56 dex, and this abundance is significantly higher than the A(Li) of the two comparison stars in NGC 2423. All three SSC hosts have the highest A(Li) and {sup 12}C/{sup 13}C when compared to the control RGs in their respective clusters; however, except for NGC 2423 3, at least one control star has similarly high abundances within the uncertainties. Higher A(Li) could suggest that the formation or presence of planets plays a role in the degree of internal mixing on or before the RG branch. However, a multitude of factors affect A(Li) during the RG phase, and when the abundances of our sample are compared with the abundances of RGs in other open clusters available in the literature, we find that they all fall well within a much larger distribution of A(Li) and {sup 12}C/{sup 13}C. Thus, even the high Li in NGC 2423 3 cannot be concretely tied to the presence of the SSC.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2016

Lithium in Open Cluster Red Giants Hosting Substellar Companions

We have measured stellar parameters, [Fe/H], lithium abundances, rotation, and (12)C/13C in a small sample of red giants (RGs) in three open clusters that are each home to a RG star that hosts a substellar companion (SSC) (NGC 2423 3, NGC 4349 127, and BD+12 1917 in M67). Our goal is to explore whether the presence of SSCs influences the Li content. Both (12)C/13C and stellar rotation are measured as additional tracers of stellar mixing. One of the companion hosts, NGC 24233, is found to be Li-rich with A(Li)(sub NLTE) = 1.56 dex, and this abundance is significantly higher than the A(Li) of the two comparison stars in NGC 2423. All three SSC hosts have the highest A(Li) and (12)C/13C when compared to the control RGs in their respective clusters; however, except for NGC 24233, at least one control star has similarly high abundances within the uncertainties. Higher A(Li) could suggest that the formation or presence of planets plays a role in the degree of internal mixing on or before the RG branch. However, a multitude of factors affect A(Li) during the RG phase, and when the abundances of our sample are compared with the abundances of RGs in other open clusters available in the literature, we find that they all fall well within a much larger distribution of A(Li) and (12)C/13C. Thus, even the high Li in NGC 2423 3 cannot be concretely tied to the presence of the SSC.

stellar parameters↗
DOE OSTI2014

An HST COS 'SNAPSHOT' spectrum of the K supergiant λ Vel (K4Ib-II)

We present a far-ultraviolet spectrum of the K4 Ib-II supergiant λ Vel obtained with the Hubble Space Telescope's Cosmic Origins Spectrograph (COS) as a part of the SNAPshot program 'SNAPing coronal iron' (GO 11687). The observation covers a wavelength region (1326-1467 Å) not previously recorded for λ Vel at a spectral resolving power of R ∼ 20,000 and displays strong emission and absorption features, superposed on a bright chromospheric continuum. Fluorescent excitation is responsible for much of the observed emission, mainly powered by strong H I Lyα and the O I (UV 2) triplet emission near λ1304. The molecular CO and H{sub 2} fluorescences are weaker than in the early-K giant α Boo while the Fe II and Cr II lines, also pumped by H I Lyα, are stronger in λ Vel. This pattern of relative line strengths between the two stars is explained by the lower iron-group element abundance in α Boo, which weakens that star's Fe II and Cr II emission without reducing the molecular fluorescences. The λ Vel spectrum shows fluorescent Fe II, Cr II, and H{sub 2} emission similar to that observed in the M supergiant α Ori, but more numerous well-defined narrow emissions from CO. The additional CO emissions are visible in the spectrum of λ Vel since that star does not have the cool, opaque circumstellar shells that surround α Ori and produce broad circumstellar CO (A-X) band absorptions that hide those emissions in the cooler star. The presence of Si IV emission in λ Vel indicates a ∼8 × 10{sup 4} K plasma that is mixed into the cooler chromosphere. Evidence of the stellar wind is seen in the C II λλ1334,1335 lines and in the blueshifted Fe II and Ni II wind absorption lines. Line modeling using Sobolev with Exact Integration for the C II lines indicates a larger terminal velocity (∼45 versus ∼30 km s{sup –1}) and turbulence (∼27 versus <21 km s{sup –1}) with a more quickly accelerating wind (β = 0.35 versus 0.7) at the time of this COS observation in 2010 than derived from Goddard High Resolution Spectrograph data obtained in 1994. The Fe II and Ni II absorptions are blueshifted by 7.6 km s{sup –1} relative to the chromospheric emission, suggesting formation in lower levels of the accelerating wind and their widths indicate a higher turbulence in the λ Vel wind compared to α Ori.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2012

OpTIIX: An ISS-Based Testbed Paving the Roadmap Toward a Next Generation Large Aperture UV/Optical Space Telescope

The next generation large aperture UV/Optical space telescope will need a diameter substantially larger than even that of JWST in order to address some of the most compelling unanswered scientific quests. These quests include understanding the earliest phases of the Universe and detecting life on exo-planets by studying spectra of their atmospheres. Such 8-16 meter telescopes face severe challenges in terms of cost and complexity and are unlikely to be affordable unless a new paradigm is adopted for their design and construction. The conventional approach is to use monolithic or preassembled segmented mirrors requiring complicated and risky deployments and relying on future heavy-lift vehicles, large fairings and complex geometry. The new paradigm is to launch component modules on relatively small vehicles and then perform in-orbit robotic assembly of those modules. The Optical Testbed and Integration on ISS eXperiment (OpTIIX) is designed to demonstrate, at low cost by leveraging the infrastructure provided by ISS, telescope assembly technologies and end-to-end optical system technologies. The use of ISS as a testbed permits the concentration of resources on reducing the technical risks associated with robotically integrating the components. These include laser metrology and wavefront sensing and control (WFS&C) systems, an imaging instrument, lightweight, low-cost deformable primary mirror segments and the secondary mirror. These elements are then aligned to a diffraction-limited optical system in space. The capability to assemble the optical system and remove and replace components via the existing ISS robotic systems like the Special Purpose Dexterous Manipulator (SPDM), or by the ISS flight crew, allows for future experimentation, as well as repair.

Carpenter, Kenneth G.↗
NASA NTRS2012

The Stellar Imager (SI) - A Mission to Resolve Stellar Surfaces, Interiors, and Magnetic Activity

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI will enable the development and testing of a predictive dynamo model for the Sun, by observing patterns of surface activity and imaging of the structure and differential rotation of stellar interiors in a population study of Sun-like stars to determine the dependence of dynamo action on mass, internal structure and flows, and time. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled processes in the Universe. SI is a "LandmarklDiscovery Mission" in the 2005 Heliophysics Roadmap, an implementation of the UVOI in the 2006 Astrophysics Strategic Plan, and a NASA Vision Mission ("NASA Space Science Vision Missions" (2008), ed. M. Allen). We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission

Christensen-Dalsgaard, Jorgen↗
NASA NTRS2010

A SNAPshot of the FUV (1320 - 1460 A) Spectrum of Lambda Vel (K4Ib-II)

The FUV spectrum (l330-1460A) of the K4Ib-II supergiant Lambda Vel was observed with the Cosmic Origins Spectrograph (COS) on HST, as part of the Ayres and Redfield Cycle 17 SNAP program "SNAPing Coronal Iron". This spectrum covers a region not previously seen in Lambda Vel at high resolution and reveals a rich emission-line spectrum superposed on a bright continuum, with contributions from a variety of atomic and molecular sources. Evidence of the stellar wind is seen in the P Cygni profiles of selected lines and the results of fluorescence processes are visible throughout the region. The spectrum has remarkable similarities to that of Alpha Boo (K1.5 III), but significant differences as well, including substantial FUV continuum emission, reminiscent of the M2 lab supergiant Alpha Ori, but minus the CO fundamental absorption bands seen in the latter star. However, fluoresced CO emission is present and strong, as in the K-giant stars Alpha Boo and Alpha Tau (K5 III). We present the details of this spectrum, in comparison to stars of similar temperature or luminosity and discuss the implications for the structure of and the radiative processes active in, the outer atmospheres of these stars.

Carpenter, Kenneth G.↗
NASA NTRS2009

Stellar Imager (SI): Enhancements to the Mission Enabled by the Constellation Architecture (Ares I/Ares V)

Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) with over 200x the resolution of HST. It will enable 0.1 milli-aresec spectral imaging of stellar surfaces and the Universe in general and open an enormous new "discovery space" for astrophysics with its combination of high angular resolution, dynamic imaging , and spectral energy resolution. SI's goal is to study the role of magnetism in the Universe and revolutionize our understanding of 1) Solar/Stellar Magnetic Activity and their impact on Space Weather, Planetary Climates, and Life, 2) Magnetic and Accretion Processes and their roles in the Origin & Evolution of Structure and in the Transport of Matter throughout the Universe, 3) the close-in structure of Active Galactic Nuclei and their winds, and 4) Exo-Solar Planet Transits and Disks. SI is a "Landmark-Discovery Mission" in 2005 Heliophysics Roadmap and a candidate UVOI in the 2006 Astrophysics Strategic Plan and is targeted for launch in the mid-2020's. It is a NASA Vision Mission and has been recommended for further study in a 2008 NRC report on missions potentially enabled/enhanced by an Ares V launch. In this paper, we discuss the science goals and required capabilities of SI, the baseline architecture of the mission assuming launch on one or more Delta rockets, and then the potential significant enhancements to the SI science and mission architecture that would be made possible by a launch in the larger volume Ares V payload fairing, and by servicing options under consideration in the Constellation program.

Carpenter, Kenneth G.↗
NASA NTRS2008

The Atmospheric Dynamics of alpha Tau (K5 III) - Clues to Understanding the Magnetic Dynamo in Late-Type Giant Stars

Using HST/GHRS, HST/STIS and FUSE archival data for alpha Tau and the CHIANTI spectroscopic code, we have derived line shifts, volumetric emission measures, and plasma density estimates, and calculated filling factors for a number of UV lines forming between 10,000 K and 300,000 K in the outer atmosphere of this red giant star. The data suggest the presence of low-temperature extended regions and high-temperature compact regions, associated with magnetically open and closed structures in the stellar atmosphere, respectively. The signatures of UV lines from alpha Tau can be consistently understood via a model of upward-traveling Alfven waves in a gravitationally stratified atmosphere. These waves cause non-thermal broadening in UV lines due to unresolved wave motions and downward plasma motions in compact magnetic loops heated by resonant Alfven wave heating.

Carpenter, Kenneth G.↗
NASA NTRS2008

The Atmospheric Dynamics of Alpha Tau (K5 III) - Clues to Understanding the Magnetic Dynamo in Late-Type Giant Stars

Using HST/GHRS, HST/STIS and FUSE archival data for a Tau and the CHIANTI spectroscopic code, we have derived line shifts, volumetric emission measures, and plasma density estimates, and calculated filling factors for a number of UV lines forming between 10,000 K and 300,000 K in the outer atmosphere of this red giant star. The data suggest the presence of low-temperature extended regions and high-temperature compact regions, associated with magnetically open and closed structures in the stellar atmosphere, respectively. The signatures of UV lines from a Tau can be consistently understood via a model of upward-traveling Alfv6n waves in a gravitationally stratified atmosphere. These waves cause nonthermal broadening in UV lines due to unresolved wave motions and downward plasma motions in compact magnetic loops heated by resonant Alfven wave heating.

Carpenter, Kenneth G.↗
NASA NTRS2008

The Stellar Imager (SI) Project: A Deep Space UV/Optical Interferometer (UVOI) to Observe the Universe at 0.1 Milli-Arcsec Angular Resolution

The Stellar Imager (SI) is a space-based, UV/ Optical Interferometer (UVOI) designed to enable 0.1 milliarcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding, of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes, such as accretion, in the Universe. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI is a "Flagship and Landmark Discovery Mission" in the 2005 Heliophysics Roadmap and a potential implementation of the UVOI in the 2006 Science Program for NASA's Astronomy and Physics Division. We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this missin. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

Carpenter, Kenneth G.↗
NASA NTRS2008

The Atmospheric Dynamics of alpha Tau (K5 III) - Clues to Understanding the Magnetic Dynamo in Late-Type Giant Stars

Using HST/GHRS, HST/STIS and FUSE archival data for alpha Tau and the CHIANTI spectroscopic code, we have derived line shifts, volumetric emission measures, and plasma density estimates, and calculated filling factors for a number of UV lines forming between 10,000 K and 300,000 K in the outer atmosphere of this red giant star. The data suggest the presence of low-temperature extended regions and high-temperature compact regions, associated with magnetically open and closed structures in the stellar atmosphere, respectively. The signatures of UV lines from alpha Tau can be consistently understood via a model of upward-traveling Alfven waves in a gravitationally stratified atmosphere. These waves cause non-thermal broadening in UV lines due to unresolved wave motions and downward plasma motions in compact magnetic loops heated by resonant Alfven wave heating.

Carpenter, Kenneth G.↗
NASA NTRS2008

Heavy Elements and Cool Stars

We report on progress in the analysis of high-resolution near-IR spectra of alpha Orionis (M2 Iab) and other cool, luminous stars. Using synthetic spectrum techniques, we search for atomic absorption lines in the stellar spectra and evaluate the available line parameter data for use in our abundance analyses. Our study concentrates on the post iron-group elements copper through zirconium as a means of investigating the slow neutron-capture process of nucleosynthesis in massive stars and the mechanisms that transport recently processed material up into the photospheric region. We discuss problems with the atomic data and model atmospheres that need to be addressed before theoretically derived elemental abundances from pre-supernova nucleosynthesis calculations can be tested by comparison with abundances determined from observations of cool, massive stars.

Wahlgren, Glenn M.↗