Pi Herculis

Pi Herculis
Pi Herculis
ClassificazioneGigante brillante arancione
Classe spettraleK3II
Distanza dal Sole370 anni luce
CostellazioneErcole
Coordinate
(all'epoca J2000)
Ascensione retta17h 15m 02,83436s
Declinazione+36° 48′ 32,9843″
Dati fisici
Raggio medio72 R⊙
Massa
4,5 M⊙
Temperatura
superficiale
  • 4110 K (media)
Luminosità
1530 L⊙
Età stimata140 milioni di anni
Dati osservativi
Magnitudine app.+3,16
Magnitudine ass.-2,15
Parallasse8,66 mas
Moto proprioAR: -27,29 mas/anno
Dec: 2,82 mas/anno
Velocità radiale-25,57 Km/s
Nomenclature alternative
67 Her, HR 6418, HD 156283, SAO 65890, BD+36°2844, FK5 643, HIP 84380.
Modifica dati su Wikidata · Manuale

Pi Herculis (π Her, π Herculis) è una stella situata nella costellazione di Ercole, distante 370 anni luce dal sistema solare. Di magnitudine apparente +3,16, nonostante abbia ricevuto la lettera greca π, è la quarta stella più luminosa della costellazione[1].

Osservazione

Si tratta di una stella situata nell'emisfero celeste boreale. La sua posizione moderatamente boreale fa sì che questa stella sia osservabile specialmente dall'emisfero nord, in cui si mostra alta nel cielo nella fascia temperata; dall'emisfero australe la sua osservazione risulta invece più penalizzata, specialmente al di fuori della sua fascia tropicale. Essendo di magnitudine 3,16, la si può osservare anche dai piccoli centri urbani senza difficoltà, sebbene un cielo non eccessivamente inquinato sia maggiormente indicato per la sua individuazione.

Il periodo migliore per la sua osservazione nel cielo serale ricade nei mesi compresi fra aprile e ottobre; nell'emisfero nord è visibile anche per un periodo maggiore, grazie alla declinazione boreale della stella, mentre nell'emisfero sud può essere osservata solo durante i mesi d'inizio estate australi.

Caratteristiche fisiche

Pi Herculis è una gigante brillante arancione di tipo spettrale K3II; possiede una massa 4,5 volte quella del Sole ed un raggio stimato da 55 a 72 volte quello solare, mentre l'età è stimata essere circa 140 milioni di anni[1]. Ha una luminosità 1500 volte e oltre quella solare, ed una magnitudine assoluta di -2,15[2].

La velocità di rotazione è molto bassa e misura circa 15 km/s[3], così come la metallicità e l'abbondanza di magnesio, che si calcolano essere rispettivamente [Fe/H]=-0,07[4] e [Mg/Fe]=-0,08[4].

Sistema planetario?

Piccole variazioni della velocità radiale della stella con periodi di 613 giorni[5] hanno suggerito la presenza di un compagno substellare. Se così fosse, probabilmente si tratterebbe di una nana bruna di almeno 27 masse gioviane distante 3 UA dalla stella principale[5]. L'ipotesi dell'oggetto substellare non è stata confermata e resta solo una possibile causa del cambiamento della velocità radiale di Pi Herculis.

Note

  1. ^ a b Pi Herculis (Stars, Jim Kaler)
  2. ^ Extended Hipparcos Compilation (XHIP) (Anderson+, 2012)
  3. ^ Catalog of Stellar Rotational Velocities (Glebocki+ 2005)
  4. ^ a b Mg/Fe ratio of MILES stars (Milone+, 2011)
  5. ^ a b Hatzes, Artie P.; Cochran, William D., Long-period, low-amplitude radial velocity variations in the K giant star pi Herculis: rotation, substellar companion or non-radial pulsations?, in Monthly Notices of the Royal Astronomical Society, vol. 304, marzo 1999, pp. 109-118, DOI:10.1046/j.1365-8711.1999.02288.x.

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