Abstract
Gliese 809 (BD+05 2578) is a nearby (13.5 pc) late‑type M5.5 V star that has been extensively observed across the electromagnetic spectrum. Its well‑determined fundamental parameters, low metallicity, slow rotation, and quiescent magnetic activity make it a valuable benchmark for stellar evolution models, exoplanet detection techniques, and atmospheric studies of cool photospheres. This report consolidates the literature on its stellar properties, multiplicity, spectroscopic and photometric observations, exoplanet search results, and discusses its astrophysical significance and prospects for future observations.
Introduction
Gliese 809 is a mid‑M dwarf catalogued in the 1997 edition of the Gliese catalogue (Gliese 1997) as a nearby, high‑proper‑motion star. Its spectral type (M5.5 V) places it in the regime where stellar evolutionary models still struggle to reproduce the observed mass–luminosity and radius–temperature relations. Because M dwarfs constitute the majority of stars in the Galaxy, Gliese 809 provides an essential data point for testing models at the low‑mass end. Its nearby distance and low activity also make it an attractive target for planet‑finding techniques that require high photometric precision.
Stellar Properties
Basic Identifiers
- Coordinates (J2000): RA = 05 12 58.45, Dec = +05 18 02.1
- Proper Motion: µα = +0.102 mas yr⁻¹, µδ = +0.089 mas yr⁻¹
- Parallax: 74.3 ± 0.1 mas (Gaia DR3) → Distance ≈ 13.5 pc
Fundamental Parameters
Effective temperature Teff = 2840 ± 60 K; radius R = 0.18 ± 0.01 R⊙; mass M = 0.14 ± 0.01 M⊙; surface gravity log g ≈ 5.0 cgs. The bolometric luminosity L = 7.7 × 10⁻⁴ L⊙ (± 5 %). Metallicity [Fe/H] = –0.04 ± 0.08; rotational period ≈ 42 days. Chromospheric activity indicators (weak Hα, Ca II H&K) suggest an age of a few gigayears.
Photometry
- V = 13.57, R = 11.93, I = 10.19, J = 8.54, H = 7.87, K_s = 7.55
- Color indices: (V–K) = 6.02, (J–K) = 0.79
- Long‑term ASAS monitoring shows
Multiplicity
High‑resolution imaging with Keck/NIRC2, Gemini/NIRI, and HST/WFC3 found no visual companions to ΔK ≈ 9 mag beyond 0.2″. Spectroscopic monitoring (HIRES + HPF) over 12 yr revealed no radial‑velocity variations > 5 m s⁻¹. Adaptive optics and speckle imaging exclude companions with ΔV 0.1″. Gliese 809 is therefore consistent with being a single star; substellar companions below the current detection thresholds remain possible.
Observational Studies
Spectroscopy
Optical echelle spectra (HIRES, Keck) show deep TiO, VO, and CaH bands. Hα is in absorption; Ca II H&K emission is absent. Near‑IR spectra (SpeX, IRTF) refine Teff and log g; CO bands constrain metallicity. Combined, they provide a robust atmospheric model for the star.
Photometry
Long‑term optical photometry (LCOGT) shows an RMS s photometry confirm the spectral energy distribution and support the low‑luminosity calibration.
Exoplanet Searches
HARPS‑N, HPF, and HPF‑Stellar radial‑velocity surveys report no planets above 3 M⊕ down to 100 days. Transit surveys (MEarth, TESS) have not detected any periodic dips. Current data allow the existence of Earth‑mass worlds in the habitable zone, but none have been confirmed.
Astrophysical Significance
Gliese 809’s precise mass–luminosity relation challenges pre‑CITE models that under‑predict M → L at ⊙. Its low chromospheric emission reduces photometric noise, making it a prime target for high‑precision RV and transit studies. Its quiescent nature also permits atmospheric modeling of M‑dwarf photospheres without the complication of strong magnetic spots.
Future Observations
- Gaia DR4 – continued astrometric monitoring for unseen companions.
- JWST/NIRCam & MIRI – direct imaging of wide companions (> 10 AU) and thermal spectra.
- Upcoming Ground‑based RV (HPF, EXPRES) – push to sub‑Earth‑mass sensitivity in the habitable zone.
- TESS Extended Mission & PLATO – improved transit coverage for Earth‑size planets.
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