{"release":{"id":"DR1","released_on":"2026-08-21","doi":null,"url":"https://spacecatalog.org/releases#dr1"},"epoch":{"requested":"now","label":"J2026.845","julian_year":2026.845,"time":"2026-11-05T12:16:32.145Z","years_from_j2000":26.845,"frame":"date","applied":"Proper motion, then precession and nutation. The catalogued position is carried along the great circle the object's own published motion puts it on, at a constant velocity, from the epoch that position was measured at, and the result is referred to the true equator and equinox of this instant. Those are separate things: the motion moves the object, and the rotation turns the grid under it by about fifty arcseconds a year, with nutation adding up to another seventeen.","excluded":"Parallax, the radial-velocity perspective term, aberration and refraction; each is below the accuracy of the catalogued positions themselves. An object with no published proper motion comes back where the catalogue has it rather than at a fabricated zero, and says so with a null pm_ra_mas_yr. The motion runs from position_epoch_jyear where the upstream publishes one — a timed pulsar's position belongs to the year it was timed — and from J2000 where it does not. A body with no fixed position is not propagated at all — its place comes from an ephemeris, which is what /api/v1/visible answers with."},"slug":"hd-28546","name":"81 Tau","class":"ka3ha8mf3_white_star","category":"star","object_type":"kA3hA8mF3 white star","mag":5.47,"mag_band":"V","abs_mag":2.208,"abs_mag_band":"V","distance_ly":146.52118649995896,"distance_method":"parallax","ra_deg":67.66203980178955,"dec_deg":15.691879,"epoch_ra_deg":68.047826,"epoch_dec_deg":15.750344,"epoch_moved_arcsec":2.871,"pm_ra_mas_yr":104.17,"pm_dec_mas_yr":-24.29,"position_epoch_jyear":null,"orbits":null,"semi_major_axis_km":null,"periapsis_km":null,"mass_kg":null,"mass_msun":null,"constellation":"Taurus","discovered":null,"featured":false,"url":"https://spacecatalog.org/object/hd-28546","source":{"id":"hyg","name":"HYG Database v4.1","url":"https://github.com/astronexus/HYG-Database","license":"CC-BY-SA-4.0","attribution":"HYG Database v4.1, Astronexus (github.com/astronexus/HYG-Database). Fields derived from it stay under CC BY-SA 4.0.","commercial_use":"allowed"},"radius_km":null,"radius_kind":null,"data_quality":null,"description":null,"properties":{"wds_id":"04306+1542","age_years":1045763400,"companions":[{"measured":2015,"magnitude":8.94,"components":"CH","discoverer_code":"BUP  62","separation_arcsec":162.3,"position_angle_deg":339},{"measured":2014,"magnitude":9.77,"components":"CJ","discoverer_code":"ARN  36","separation_arcsec":397.8,"position_angle_deg":36},{"measured":2014,"magnitude":5.7,"components":"CI","discoverer_code":"ARN  36","separation_arcsec":484.5,"position_angle_deg":246}],"mass_solar":1.691,"radius_solar":1.929,"spectral_type":"kA3hA8mF3","uncertainties":{"distance_ly":[3.1558430354788896,3.297906709101726],"metallicity_fe_h":[0.145,0.145]},"color_index_bv":0.258,"luminosity_solar":11.39724804019748,"metallicity_fe_h":0.24,"radial_velocity_km_s":39,"spectral_type_source":"SIMBAD (1999A&AS..137..451G, quality D)","surface_gravity_log_g":4.042,"surface_temperature_k":7510,"metallicity_fe_h_source":"Median of 3 spectroscopic determinations in 3 papers, compiled from the literature (PASTEL, Soubiran+ 2016); the error bar is the scatter between them","proper_motion_ra_mas_yr":104.17,"proper_motion_dec_mas_yr":-24.29,"stellar_parameters_method":"Gaia DR3 model fit (GSP-Phot, FLAME; RUWE ≤ 1.4) — low confidence: above 7,500 K GSP-Phot's temperature and extinction are degenerate","bolometric_luminosity_solar":10.6623},"designations":[{"catalog":"Bayer/Flamsteed","designation":"81 Tau"},{"catalog":"HD","designation":"HD 28546"},{"catalog":"HIP","designation":"HIP 21039"},{"catalog":"HR","designation":"HR 1428"}],"updated_at":"2026-11-04T19:31:31.075Z","citation":{"plain":"SpaceCatalog. 81 Tau [catalogue entry]. Data release DR1 (2026-08-21). https://spacecatalog.org/object/hd-28546","bibtex":"@misc{spacecatalog_hd-28546,\n  author       = {{SpaceCatalog}},\n  title        = {{81 Tau}},\n  howpublished = {SpaceCatalog, data release DR1 (2026-08-21)},\n  year         = {2026},\n  url          = {https://spacecatalog.org/object/hd-28546},\n  note         = {Catalogue entry, data release DR1 (2026-08-21). Values from HYG Database v4.1.}\n}","url":"https://spacecatalog.org/object/hd-28546","release":"DR1","doi":null},"references":[{"bibcode":"1999A&AS..137..451G","ads_url":"https://ui.adsabs.harvard.edu/abs/1999A%26AS..137..451G/abstract","quantity":"properties.spectral_type_source"}],"attribution":"Data from SpaceCatalog.org. Each record names its upstream in `source`, with that producer's terms in `source.license`, the acknowledgement it asks for in `source.attribution`, and whether its terms allow commercial use in `source.commercial_use`; those terms govern the record, and citing SpaceCatalog does not discharge them."}