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| Alpha Andromedae | |
|---|---|
| Name | Alpha Andromedae |
| Other names | Alpheratz, Sirrah, HR 15, HD 358 |
| Constellation | Andromeda |
| Epoch | J2000 |
| Apparent magnitude | 2.06 |
| Spectral type | B8IVpMnHg |
| Distance | 97 ly |
| Radial velocity | −12 km/s |
| Components | binary (Aa, Ab) |
Alpha Andromedae Alpha Andromedae is a bright, blue-white star traditionally called Alpheratz and Sirrah that marks the head of the Andromeda figure and forms the northeast corner of the Great Square of Pegasus. It has been catalogued in historical works such as the Almagest and by astronomers including Ptolemy, Johann Bayer, John Flamsteed, and later in modern catalogs such as the Henry Draper Catalogue and the Hipparcos mission. The star is notable in observational astronomy, stellar spectroscopy, and studies of chemically peculiar stars, attracting attention from observatories like Greenwich Observatory, Harvard College Observatory, and facilities using instruments on ESO telescopes.
The traditional names Alpheratz and Sirrah derive from Arabic and entered western charts via translations connected to scholars such as Gerard of Cremona and Johannes Hevelius, while catalog designations include systems by Bayer, Flamsteed, and the Bright Star Catalogue. Early astrometry was performed by observers associated with Ptolemy and later refined by Tycho Brahe, John Flamsteed, and the Uranometria tradition; modern parallaxes were measured by Hipparcos and confirmed by Gaia. Spectroscopic study began with classifications in the era of Annie Jump Cannon and Edward Pickering, followed by detailed abundance analyses using equipment at Mount Wilson Observatory and Palomar Observatory.
The star is a close binary comprising a visually dominant B-type primary and a fainter companion first resolved through combined spectroscopic and interferometric work performed by teams associated with VLT-class interferometers, radio arrays, and speckle programs at institutions like Kitt Peak National Observatory and Cerro Tololo Inter-American Observatory. The system has been included in catalogs such as the CCDM and studied by researchers affiliated with Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute for Astronomy. Observations contributing to orbital solutions have been published by consortia linked to IAU symposia and the American Astronomical Society.
Spectral classification places the primary near B8IVpMnHg, a late-B subgiant noted in work by Morgan–Keenan classifiers and analysts from the Copenhagen Observatory. Its effective temperature, luminosity, radius, and mass estimates derive from stellar models used by researchers at Cambridge University, Princeton University, and California Institute of Technology, and are constrained by photometry from missions like Tycho and 2MASS. Evolutionary status has been discussed in publications associated with the Geneva stellar evolution models and groups from University of Geneva and Observatoire de Paris.
The primary is a mercury-manganese chemically peculiar star first characterized in abundance surveys conducted at Harvard College Observatory and later with high-resolution spectroscopy at European Southern Observatory and Keck Observatory. Detailed line analyses revealing overabundances of elements such as mercury and manganese were reported by teams connected to Royal Astronomical Society, Max Planck Institute for Astronomy, and researchers collaborating with Smithsonian Institution spectrographs. Unlike classical magnetic Ap stars studied by groups at Paris Observatory and Leiden Observatory, the star exhibits weak or complex magnetic signatures investigated by projects using polarimeters developed at Institut d'Astrophysique de Paris and instruments motivated by work at NRAO.
Photometric monitoring from networks such as the AAVSO, space missions like Hipparcos and TESS, and ground campaigns at Las Campanas Observatory has revealed low-amplitude variability linked to rotational modulation and surface abundance patches, paralleling studies of variability in stars reported by Royal Astronomical Society journals and teams from University of Vienna and University of Toronto. Period analyses have been published in conferences organized by the IAU and by researchers affiliated with ESA programs.
Parallax and proper motion measurements from Hipparcos and refined by Gaia provide distance and kinematic parameters used in galactic context studies by groups at Max Planck Institute for Astrophysics and Leiden University. Radial velocity studies connected to long-term surveys at Calar Alto Observatory and Mount Stromlo Observatory have contributed to the orbital solution, which has been modeled using techniques developed at University of Cambridge and applied in collaborative projects involving ESO and the CNRS.