The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
William D. Vacca - One of the best experts on this subject based on the ideXlab platform.
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The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
The Astrophysical Journal Supplement Series, 2009Co-Authors: John T. Rayner, Michael C. Cushing, William D. VaccaAbstract:We present a 0.8 -5 micron spectral library of 210 Cool Stars observed at a resolving power of R = lambda / Delta lambda ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The Stars have well established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S Stars. In contrast to some other spectral libraries, the continuum shape of the spectra are measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using Two Micron All Sky Survey (2MASS) photometry. Potential uses of the library include studying the physics of Cool Stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically-obscured regions of galaxies, and synthetic photometry. The library is available in digital form from the IRTF website.
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the infrared telescope facility irtf spectral library Cool Stars
Astrophysical Journal Supplement Series, 2009Co-Authors: John T. Rayner, Michael C. Cushing, William D. VaccaAbstract:We present a 0.8-5 μm spectral library of 210 Cool Stars observed at a resolving power of R ≡ λ/Δλ ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The Stars have well-established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample not only contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S Stars. In contrast to some other spectral libraries, the continuum shape of the spectra is measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using the Two Micron All Sky Survey photometry. Potential uses of the library include studying the physics of Cool Stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically obscured regions of galaxies and synthetic photometry. The library is available in digital form from the IRTF Web site.
John T. Rayner - One of the best experts on this subject based on the ideXlab platform.
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The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
The Astrophysical Journal Supplement Series, 2009Co-Authors: John T. Rayner, Michael C. Cushing, William D. VaccaAbstract:We present a 0.8 -5 micron spectral library of 210 Cool Stars observed at a resolving power of R = lambda / Delta lambda ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The Stars have well established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S Stars. In contrast to some other spectral libraries, the continuum shape of the spectra are measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using Two Micron All Sky Survey (2MASS) photometry. Potential uses of the library include studying the physics of Cool Stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically-obscured regions of galaxies, and synthetic photometry. The library is available in digital form from the IRTF website.
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the infrared telescope facility irtf spectral library Cool Stars
Astrophysical Journal Supplement Series, 2009Co-Authors: John T. Rayner, Michael C. Cushing, William D. VaccaAbstract:We present a 0.8-5 μm spectral library of 210 Cool Stars observed at a resolving power of R ≡ λ/Δλ ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The Stars have well-established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample not only contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S Stars. In contrast to some other spectral libraries, the continuum shape of the spectra is measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using the Two Micron All Sky Survey photometry. Potential uses of the library include studying the physics of Cool Stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically obscured regions of galaxies and synthetic photometry. The library is available in digital form from the IRTF Web site.
A.k. Dupree - One of the best experts on this subject based on the ideXlab platform.
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Chromospheres of Luminous Cool Stars
Proceedings of the International Astronomical Union, 2015Co-Authors: A.k. DupreeAbstract:AbstractDirect ultraviolet imaging and spectroscopy of Alpha Orionis (Betelgeuse) reveals variable chromospheric structures and mass motions. Spectroscopy also demonstrates the changes of wind opacity, speeds, and mass loss in luminous Stars. Cool Stars have complex chromospheres that need to be considered in construction of stellar atmospheric models and subsequent spectral analyses.
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Summary Highlights from Cool Stars 15
AIP Conference Proceedings, 2009Co-Authors: A.k. DupreeAbstract:A Summary of some scientific highlights of Cool Stars 15 and reflections, as well as awards and a quiz for the participants.
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Active Cool Stars and He I 10830 \AA: the coronal connection
Astronomy & Astrophysics, 2008Co-Authors: J. Sanz-forcada, A.k. DupreeAbstract:The mechanism of formation of the He I 10830 A triplet in Cool Stars has been subject of debate for the last 30 years. A relation between the X-ray luminosity and the He I 10830 A flux was found in Cool Stars, but the dominant mechanism of formation in these Stars (photoionization by coronal radiation followed by recombination and cascade, or collisional excitation in the chromosphere), has not yet been established. We use modern instrumentation (NOT/SOFIN) and a direct measurement of the EUV flux, which photoionizes He I, to investigate the formation mechanism of the line for the most active Stars which are frequently excluded from analysis. We have observed with an unprecedented resolution (R~170,000) the He I 10830 A triplet in a set of 15 Stars that were also observed with the Extreme Ultraviolet Explorer (EUVE) in order to compare the line strengths with their EUV and X-ray fluxes. Active dwarf and subgiant Stars do not exhibit a relation between the EUV flux and the equivalent width of the He I 10830 A line. Giant Stars however, show a positive correlation between the strength of the He I 10830 A absorption and the EUV and X-ray fluxes. The strength of the C IV 1550 A emission does not correlate with coronal fluxes in this sample of 15 Stars. Active dwarf Stars may have high chromospheric densities thus allowing collisional excitation to dominate photoionization/recombination processes in forming the He I 10830 A line. Active giant Stars possess lower gravities, and lower chromospheric densities than dwarfs, allowing for photoexcitation processes to become important. Moreover, their extended chromospheres allowfor scattering of infrared continuum radiation, producing strong absorption in He I and tracing wind dynamics.
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Winds from Cool Stars
Symposium - International Astronomical Union, 2004Co-Authors: A.k. DupreeAbstract:Recent spectroscopic results from the far ultraviolet and X-ray region coupled with infrared observations demonstrate that winds from luminous Stars can be warm (300000K) and fast (speeds of several hundred km s—1) linking the hot solar wind to the Cool, massive winds of luminous M-type supergiant Stars. Hot coronal material (T ∼107 K) appears to be confined near the star, and not expanding in the wind. These new spectra enable a comprehensive picture to be constructed of the presence and character of winds in Cool Stars.
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Winds from Cool Stars
AIP Conference Proceedings, 1996Co-Authors: A.k. DupreeAbstract:Spectral observations of Cool Stars enable the study of the presence and character of winds and the mass loss process in objects with effective temperatures, gravities, and atmospheric compositions which differ from that of the Sun. A wealth of recent spectroscopic measurements from the Hubble Space Telescope, and the Extreme Ultraviolet Explorer satellite complement high resolution ground-based spectra in the optical and infrared spectral regions. Such observations when combined with realistic semi-empirical atmospheric modeling allow us to estimate the physical conditions in the atmospheres and winds of many classes of Cool Stars. In low gravity Stars, evidence is found for relatively fast (≈200 km s-1), warm winds with rapid acceleration occurring in the chromosphere. In some cases, outflows commensurate with stellar escape velocities are present.
Michael C. Cushing - One of the best experts on this subject based on the ideXlab platform.
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The Infrared Telescope Facility (IRTF) Spectral Library: Cool Stars
The Astrophysical Journal Supplement Series, 2009Co-Authors: John T. Rayner, Michael C. Cushing, William D. VaccaAbstract:We present a 0.8 -5 micron spectral library of 210 Cool Stars observed at a resolving power of R = lambda / Delta lambda ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The Stars have well established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S Stars. In contrast to some other spectral libraries, the continuum shape of the spectra are measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using Two Micron All Sky Survey (2MASS) photometry. Potential uses of the library include studying the physics of Cool Stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically-obscured regions of galaxies, and synthetic photometry. The library is available in digital form from the IRTF website.
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the infrared telescope facility irtf spectral library Cool Stars
Astrophysical Journal Supplement Series, 2009Co-Authors: John T. Rayner, Michael C. Cushing, William D. VaccaAbstract:We present a 0.8-5 μm spectral library of 210 Cool Stars observed at a resolving power of R ≡ λ/Δλ ~ 2000 with the medium-resolution infrared spectrograph, SpeX, at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The Stars have well-established MK spectral classifications and are mostly restricted to near-solar metallicities. The sample not only contains the F, G, K, and M spectral types with luminosity classes between I and V, but also includes some AGB, carbon, and S Stars. In contrast to some other spectral libraries, the continuum shape of the spectra is measured and preserved in the data reduction process. The spectra are absolutely flux calibrated using the Two Micron All Sky Survey photometry. Potential uses of the library include studying the physics of Cool Stars, classifying and studying embedded young clusters and optically obscured regions of the Galaxy, evolutionary population synthesis to study unresolved stellar populations in optically obscured regions of galaxies and synthetic photometry. The library is available in digital form from the IRTF Web site.
A. P. Yadav - One of the best experts on this subject based on the ideXlab platform.
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Chromospheric activity catalogue of 4454 Cool Stars. Questioning the active branch of stellar activity cycles
Astronomy & Astrophysics, 2018Co-Authors: S. Boro Saikia, Pascal Petit, Sandra V. Jeffers, Ansgar Reiners, Christopher Marvin, Robert H. Cameron, Stephen C. Marsden, Jörn Warnecke, A. P. YadavAbstract:Chromospheric activity monitoring of a wide range of Cool Stars can provide valuable information on stellar magnetic activity and its dependence on fundamental stellar parameters such as effective temperature and rotation.We compile a chromospheric activity catalogue of 4454 Cool Stars from a combination of archival HARPS spectra and multiple other surveys, including the Mount Wilson data that have recently been released by the NSO. We explore the variation in chromospheric activity of Cool Stars along the main sequence for Stars with different effective temperatures. Additionally, we also perform an activity-cycle period search and investigate its relation with rotation. The chromospheric activity index, S-index, was measured for 304 main-sequence Stars from archived high-resolution HARPS spectra. Additionally, the measured and archived S-indices were converted into the chromospheric flux ratio log R'HK. The activity-cycle periods were determined using the generalised Lomb-Scargle periodogram to study the active and inactive branches on the rotation-activity-cycle period plane. The global sample shows that the bimodality of chromospheric activity, known as the Vaughan-Preston gap, is not prominent, with a significant percentage of the Stars at an intermediate-activity level around log R'HK = -4.75. Independently, the cycle period search shows that Stars can lie in the region intermediate between the active and inactive branch, which means that the active branch is not as clearly distinct as previously thought. The weakening of the Vaughan-Preston gap indicates that Cool Stars spin down from a higher activity level and settle at a lower activity level without a sudden break at intermediate activity. Some cycle periods are close to the solar value between the active and inactive branch, which suggests that the solar dynamo is most likely a common case of the stellar dynamo.
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chromospheric activity catalogue of 4454 Cool Stars questioning the active branch of stellar activity cycles
Astronomy and Astrophysics, 2018Co-Authors: Boro S Saikia, Christopher Marvin, Robert H. Cameron, Stephen C. Marsden, Jörn Warnecke, S V Jeffers, A Reiners, P Petit, A. P. YadavAbstract:Context. Chromospheric activity monitoring of a wide range of Cool Stars can provide valuable information on stellar magnetic activity and its dependence on fundamental stellar parameters such as effective temperature and rotation. Aims. We compile a chromospheric activity catalogue of 4454 Cool Stars from a combination of archival HARPS spectra and multiple other surveys, including the Mount Wilson data that have recently been released by the NSO. We explore the variation in chromospheric activity of Cool Stars along the main sequence for Stars with different effective temperatures. Additionally, we also perform an activity-cycle period search and investigate its relation with rotation. Methods. The chromospheric activity index, S-index, was measured for 304 main-sequence Stars from archived high-resolution HARPS spectra. Additionally, the measured and archived S-indices were converted into the chromospheric flux ratio log R0 HK. The activity-cycle periods were determined using the generalised Lomb-Scargle periodogram to study the active and inactive branches on the rotation – activity-cycle period plane. Results. The global sample shows that the bimodality of chromospheric activity, known as the Vaughan-Preston gap, is not prominent, with a significant percentage of the Stars at an intermediate-activity level around log R0 HK = -4.75. Independently, the cycle period reearch shows that Stars can lie in the region intermediate between the active and inactive branch, which means that the active branch is not as clearly distinct as previously thought. Conclusions. The weakening of the Vaughan-Preston gap indicates that Cool Stars spin down from a higher activity level and settle at a lower activity level without a sudden break at intermediate activity. Some cycle periods are close to the solar value between the active and inactive branch, which suggests that the solar dynamo is most likely a common case of the stellar dynamo.