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378 results on '"Shectman, Stephen A."'

357. MegaMapper: concept and optical design for a 6.5m aperture massively multiplexed spectroscopic facility

Author

Marshall, Heather K., Spyromilio, Jason, Usuda, Tomonori, Blanc, Guillermo A., Silber, Joseph Harry, Smee, Stephen, Barkhouser, Robert, Besuner, Robert, Crane, Jeffrey D., Kollmeier, Juna A., Palunas, Povilas, Schlegel, David, Shectman, Stephen, Araujo, Ricardo, Baltay, Charlie, Bouri, Mohamed, Farr, Emily, Guy, Julien, Infante, Leopoldo, Kneib, Jean-Paul, Mandeville, Travis, Poppett, Claire, Rabinowitz, David, Ramirez, Solange V., Schubnell, Michael, Simon, Joshua, Thurneysen, Markus, Tuttle, Sarah, Van Shourt, William, and Wachter, Stefanie

Published
2022
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360. Clusters of galaxies and the cosmic light

Author

Shectman, Stephen Alan, Shectman, Stephen Alan, Shectman, Stephen Alan, and Shectman, Stephen Alan

Abstract

Because galaxies cluster in space, the cosmic background light due to galaxies is not smoothly distributed on the night sky. Part I predicts spatial power spectra for the cosmic light fluctuations, based on the luminosity function for nearby galaxies and on the dumpiness of the galaxy distribution derived from galaxy counts. Part II describes a measurement of the spatial power spectrum of the cosmic light on a series of photographic plates taken with the Palomar 48-inch (122cm) Schmidt camera. This power spectrum is interpreted to provide a measure of the covariance of the galaxy distribution and the mean emissivity of galaxies in space.

Published
1974

362. CS 22964-161: A Double-Lined Carbon- and s-Process-Enhanced Metal-Poor Binary Star

Author

Thompson, Ian B., Ivans, Inese I., Bisterzo, Sara, Sneden, Christopher, Gallino, Roberto, Vauclair, Sylvie, Burley, Gregory S., Shectman, Stephen A., and Preston, George W.

Abstract

A detailed high-resolution spectroscopic analysis is presented for the carbon-rich low-metallicity Galactic halo object CS 22964-161. We have discovered that CS 22964-161 is a double-lined spectroscopic binary and have derived accurate orbital components for the system. From a model atmosphere analysis we show that both components are near the metal-poor main-sequence turnoff. Both stars are very enriched in carbon and in neutron-capture elements that can be created in the s-process, including lead. The primary star also possesses an abundance of lithium close to the value of the "Spite plateau." The simplest interpretation is that the binary members seen today were the recipients of these anomalous abundances from a third star that was losing mass as part of its AGB evolution. We compare the observed CS 22964-161 abundance set with nucleosynthesis predictions of AGB stars, discuss issues of envelope stability in the observed stars under mass transfer conditions, and consider the dynamical stability of the alleged original triple star. Finally, we consider the circumstances that permit survival of lithium, whatever its origin, in the spectrum of this extraordinary system.

Published
2008

363. MegaMapper: Concept and Optical Design for a 6.5 m Aperture Massively Multiplexed Spectroscopic Facility

Author

Blanc, Guillermo A., Silber, Joseph H., Smee, Stephen A., Barkhouser, Robert H., Besuner, Robert W., Crane, Jeffrey, Kollmeier, Juna, Palunas, Povilas, Schlegel, David, Shectman, Stephen, Araujo, Ricardo, Baltay, Charlie, Bouri, Mohamed, Farr, Emily, Guy, Julien, Infante, Leopoldo, Kneib, Jean-Paul, Mandeville, Travis, Poppett, Claire, Rabinowitz, David, Ramirez, Solange, Schubnell, Michael, Simon, Joshua, Thurneysen, Markus, Tuttle, Sarah, Van Shourt, William, and Wachter, Stefanie

Subjects
desi, fiber spectroscopy, wide-field correctors, wide-field telescopes, magellan telescopes, sdss-v, multi-object spectroscopy, fiber positioners, cosmology
Abstract

MegaMapper is a 6.5m Magellan-like telescope fitted with a wide-field-corrector (WFC) and atmospheric-dispersion-corrector (ADC) that delivers a 3. diameter corrected field-of-view. The telescope's focal surface is populated by similar to 25, 000 robotic fiber-positioners feeding a cluster of 36 DESI-like medium resolution spectrographs. We present the facility concept for MegaMapper including: conceptual optical and opto-mechanical designs for the telescope and WFC/ADC that deliver less than or similar to 0.4 '' image quality over the full FOV for zenith distances

375. THE CARNEGIE-SPITZER-IMACS REDSHIFT SURVEY OF GALAXY EVOLUTION SINCE z = 1.5. I. DESCRIPTION AND METHODOLOGY.

Author

Kelson, Daniel D., Williams, Rik J., Dressler, Alan, McCarthy, Patrick J., Shectman, Stephen A., Mulchaey, John S., Villanueva, Edward V., Crane, Jeffrey D., and Quadri, Ryan F.

Subjects
GALACTIC evolution, REDSHIFT, STELLAR activity, INFRARED radiation, ASTROPHYSICS
Abstract

We describe the Carnegie-Spitzer-IMACS (CSI) Survey, a wide-field, near-IR selected spectrophotometric redshift survey with the Inamori Magellan Areal Camera and Spectrograph (IMACS) on Magellan-Baade. By defining a flux-limited sample of galaxies in Spitzer Infrared Array Camera 3.6 μm imaging of SWIRE fields, the CSI Survey efficiently traces the stellar mass of average galaxies to z ∼ 1.5. This first paper provides an overview of the survey selection, observations, processing of the photometry and spectrophotometry. We also describe the processing of the data: new methods of fitting synthetic templates of spectral energy distributions are used to derive redshifts, stellar masses, emission line luminosities, and coarse information on recent star formation. Our unique methodology for analyzing low-dispersion spectra taken with multilayer prisms in IMACS, combined with panchromatic photometry from the ultraviolet to the IR, has yielded high-quality redshifts for 43,347 galaxies in our first 5.3 deg2 of the SWIRE XMM-LSS field. We use three different approaches to estimate our redshift errors and find robust agreement. Over the full range of 3.6 μm fluxes of our selection, we find typical redshift uncertainties of σz/(1 + z) ≲ 0.015. In comparisons with previously published spectroscopic redshifts we find scatters of σz/(1 + z) = 0.011 for galaxies at 0.7 ⩽ z ⩽ 0.9, and σz/(1 + z) = 0.014 for galaxies at 0.9 ⩽ z ⩽ 1.2. For galaxies brighter and fainter than i = 23 mag, we find σz/(1 + z) = 0.008 and σz/(1 + z) = 0.022, respectively. Notably, our low-dispersion spectroscopy and analysis yields comparable redshift uncertainties and success rates for both red and blue galaxies, largely eliminating color-based systematics that can seriously bias observed dependencies of galaxy evolution on environment. [ABSTRACT FROM AUTHOR]

Published
2014
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378. TOI-1075 b: A Dense, Massive, Ultra-short-period Hot Super-Earth Straddling the Radius Gap

Author

Zahra Essack, Avi Shporer, Jennifer A. Burt, Sara Seager, Saverio Cambioni, Zifan Lin, Karen A. Collins, Eric E. Mamajek, Keivan G. Stassun, George R. Ricker, Roland Vanderspek, David W. Latham, Joshua N. Winn, Jon M. Jenkins, R. Paul Butler, David Charbonneau, Kevin I. Collins, Jeffrey D. Crane, Tianjun Gan, Coel Hellier, Steve B. Howell, Jonathan Irwin, Andrew W. Mann, Ali Ramadhan, Stephen A. Shectman, Johanna K. Teske, Samuel W. Yee, Ismael Mireles, Elisa V. Quintana, Peter Tenenbaum, Guillermo Torres, Elise Furlan, Essack, Zahra [0000-0002-2482-0180], Shporer, Avi [0000-0002-1836-3120], Burt, Jennifer A [0000-0002-0040-6815], Seager, Sara [0000-0002-6892-6948], Cambioni, Saverio [0000-0001-6294-4523], Lin, Zifan [0000-0003-0525-9647], Collins, Karen A [0000-0001-6588-9574], Mamajek, Eric E [0000-0003-2008-1488], Stassun, Keivan G [0000-0002-3481-9052], Ricker, George R [0000-0003-2058-6662], Vanderspek, Roland [0000-0001-6763-6562], Latham, David W [0000-0001-9911-7388], Winn, Joshua N [0000-0002-4265-047X], Jenkins, Jon M [0000-0002-4715-9460], Butler, R Paul [0000-0003-1305-3761], Charbonneau, David [0000-0002-9003-484X], Collins, Kevin I [0000-0003-2781-3207], Crane, Jeffrey D [0000-0002-5226-787X], Gan, Tianjun [0000-0002-4503-9705], Hellier, Coel [0000-0002-3439-1439], Howell, Steve B [0000-0002-2532-2853], Mann, Andrew W [0000-0003-3654-1602], Ramadhan, Ali [0000-0003-1102-1520], Shectman, Stephen A [0000-0002-8681-6136], Yee, Samuel W [0000-0001-7961-3907], Mireles, Ismael [0000-0002-4510-2268], Quintana, Elisa V [0000-0003-1309-2904], Tenenbaum, Peter [0000-0002-1949-4720], Torres, Guillermo [0000-0002-5286-0251], Furlan, Elise [0000-0001-9800-6248], and Apollo - University of Cambridge Repository

Subjects
Earth and Planetary Astrophysics (astro-ph.EP), Space and Planetary Science, Exoplanets (498), Transit photometry (1709), Radial velocity (1332), Planetary system formation (1257), FOS: Physical sciences, Astronomy and Astrophysics, Super Earths (1655), Extrasolar rocky planets (511), Astrophysics - Earth and Planetary Astrophysics
Abstract

Populating the exoplanet mass-radius diagram in order to identify the underlying relationship that governs planet composition is driving an interdisciplinary effort within the exoplanet community. The discovery of hot super-Earths - a high temperature, short-period subset of the super-Earth planet population - has presented many unresolved questions concerning the formation, evolution, and composition of rocky planets. We report the discovery of a transiting, ultra-short period hot super-Earth orbiting TOI-1075 (TIC 351601843), a nearby ($d$ = 61.4 pc) late K-/early M-dwarf star, using data from the Transiting Exoplanet Survey Satellite (TESS). The newly discovered planet has a radius of $1.791^{+0.116}_{-0.081}$ $R_{\oplus}$, and an orbital period of 0.605 days (14.5 hours). We precisely measure the planet mass to be $9.95^{+1.36}_{-1.30}$ $M_{\oplus}$ using radial velocity measurements obtained with the Planet Finder Spectrograph (PFS), mounted on the Magellan II telescope. Our radial velocity data also show a long-term trend, suggesting an additional planet in the system. While TOI-1075 b is expected to have a substantial H/He atmosphere given its size relative to the radius gap, its high density ($9.32^{+2.05}_{-1.85}$ $\rm{g/cm^3}$) is likely inconsistent with this possibility. We explore TOI-1075 b's location relative to the M-dwarf radius valley, evaluate the planet's prospects for atmospheric characterization, and discuss potential planet formation mechanisms. Studying the TOI-1075 system in the broader context of ultra-short period planetary systems is necessary for testing planet formation and evolution theories, density enhancing mechanisms, and for future atmospheric and surface characterization studies via emission spectroscopy with JWST., 24 pages, 9 figures, 6 tables. Accepted for publication in The Astronomical Journal

Published
2023
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