Altair

Altair
Aquila_constellation_map.png: Torsten Bronger derivative work: Kxx (talk) · CC BY-SA 3.0 · source
Name	Altair
Constellation	Aquila
Spectral type	A7V
Apparent magnitude	0.77
Distance ly	16.7
Mass	1.79–1.85 M☉
Radius	1.6–2.0 R☉ (equatorial/polar)
Rotation period	8.9–10.5 hours
Other designations	Alpha Aquilae, HD 187642

Altair

Altair is a bright, nearby A-type main-sequence star in the constellation Aquila, prominent in northern summer skies and forming one vertex of the Summer Triangle alongside two other bright stars. It is one of the nearest visible stars to Earth and has been central to observational programs in stellar astrophysics, interferometry, asteroseismology, and exoplanetary searches conducted by organizations and observatories worldwide. Its rapid rotation, proximity, and brightness have made it a frequent target for instruments associated with programs at observatories such as Mount Wilson, Palomar, and facilities operated by institutions including NASA, ESA, and various universities.

Overview

Altair lies in the constellation linked historically to the figure of the eagle, and in modern catalogs it appears as Alpha Aquilae and HD 187642 in the Henry Draper Catalogue. It participates in the asterism known as the Summer Triangle with Vega and Deneb, a grouping often cited in guides by the Royal Astronomical Society, Harvard College Observatory, and amateur astronomy organizations. Because of its proximity, publications from the European Southern Observatory, National Optical Astronomy Observatory, and the International Astronomical Union have frequently included Altair in surveys of bright, nearby stars. Contemporary catalogs and missions such as Hipparcos, Tycho, and Gaia provide parallax and proper motion data used by researchers at institutions like the Space Telescope Science Institute and the Jet Propulsion Laboratory.

Physical Characteristics

Altair is classified as an A7V star in spectral catalogs compiled by the Mount Wilson and Lick Observatory spectral atlases and listed in the Bright Star Catalogue maintained by observatories tied to the Smithsonian Astrophysical Observatory. Spectroscopic studies by groups at the University of Cambridge, California Institute of Technology, and Max Planck Institute for Astronomy reveal A-type absorption lines characteristic of hydrogen and metal lines cataloged alongside work on stars such as Sirius, Procyon, and Vega. High-resolution spectroscopy from instruments on telescopes at observatories like Keck, VLT, and Subaru shows significant rotational broadening, comparable to other rapid rotators cataloged by the Royal Astronomical Society and the American Astronomical Society. Photometric monitoring by the Whole Earth Telescope consortium and missions such as WIRE and MOST has been used to assess its brightness variations in the context of catalogs that include Beta Cephei and Delta Scuti variables.

Stellar Evolution and Properties

Stellar models from research groups at Princeton University, University of California, Santa Cruz, and the Institut d'Astrophysique de Paris place Altair on the main sequence with a mass roughly between that of Pollux and Fomalhaut, and an age estimated by teams at Yale and Geneva to be hundreds of millions of years—comparable to clusters studied by observers at Mount Palomar and Cerro Tololo. Evolutionary tracks computed using codes developed at institutions such as the University of Geneva and the MESA collaboration account for rapid rotation effects also examined in research on Regulus and Achernar. Interferometric imaging results from facilities including the CHARA Array, the Palomar Testbed Interferometer, and the Very Large Telescope Interferometer have been compared with models from groups at Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute to infer gravity darkening, oblateness, and latitudinal temperature variation, phenomena also studied in other stars like Altair’s neighbors Vega and Achernar.

Observational History and Cultural Significance

Altair has a long observational record preserved in catalogs from ancient star lists, through the star charts of Tycho Brahe and Johann Bayer, into modern surveys by Hipparcos and Gaia. Its cultural roles appear in mythologies and navigation lore documented by historians at the British Museum, the Smithsonian Institution, and the Library of Congress, and it figures in works of literature analyzed by scholars at Oxford University and Harvard University. Notable observational milestones include early spectroscopic classification at Mount Wilson Observatory, interferometric imaging achievements led by teams at Georgia State University and the National Optical Astronomy Observatory, and time-series photometry campaigns coordinated by international consortia such as the Whole Earth Telescope and the American Association of Variable Star Observers.

Planetary System and Debris

Searches for companions and circumstellar material around Altair have been carried out by groups using facilities including the Hubble Space Telescope, the Spitzer Space Telescope, the Atacama Large Millimeter/submillimeter Array, and ground-based adaptive optics systems at Keck and the Gemini Observatory. Surveys by teams associated with institutions such as the SETI Institute, the Carnegie Institution for Science, and the European Southern Observatory have placed upper limits on massive planetary companions and have searched for debris analogous to the Kuiper Belt and Zodiacal dust studied in systems like Beta Pictoris and Fomalhaut. Infrared excess studies reported by researchers at Caltech and IPAC suggest no substantial warm debris disk comparable to young debris disks cataloged by the Herschel Space Observatory and the Spitzer mission, though constraints continue to be refined by ongoing programs.

Research and Modern Observations

Modern investigations of Altair involve interferometry from CHARA and VLTI, asteroseismic analyses by teams at the University of Birmingham and the University of Sydney, and high-resolution spectroscopy from observatories such as Keck and the European Southern Observatory. Data products from missions and surveys—Hipparcos, Gaia, WISE, and TESS—are used by investigators at institutions including NASA Ames Research Center, ESA Science Division, and universities worldwide to refine parameters like mass, radius, rotational profile, and pulsation modes. Collaborative projects between national observatories, university consortia, and instrument teams continue to place Altair among benchmark stars in studies alongside Vega, Sirius, and Procyon for calibrating stellar models, testing theories developed at institutes like the Max Planck Institute and CNRS, and guiding exoplanet detection strategies employed by research groups at JPL and STScI.

Category:Stars