L2 Puppis

For other stars with this Bayer designation, see L Puppis.

L₂ Puppis (also known as HD 56096) is a giant star in the constellation of Puppis and is located between the bright stars Canopus and Sirius. It is a semi-regular pulsating star, and is intermittently visible to the naked eye.

L₂ Puppis

Location of L2 Puppis (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Puppis
Right ascension	07h 13m 32.31810s[1]
Declination	−44° 38′ 23.0630″[1]
Apparent magnitude (V)	5.10[2] 2.6–6 (GCVS)[3] 6–8 (1995 – )[4]
Characteristics
Evolutionary stage	Red-giant branch[5]
Spectral type	M5IIIe[3]
U−B color index	+1.24[2]
B−V color index	+1.56[2]
Variable type	SRb[3]
Astrometry
Radial velocity (Rv)	33.0[6] km/s
Proper motion (μ)	RA: 106.31[1] mas/yr Dec.: 324.99[1] mas/yr
Parallax (π)	15.61±0.99 mas[1]
Distance	210 ± 10 ly (64 ± 4 pc)
Details
Mass	0.659±0.043[6] M☉
Radius	123±14[6] R☉
Luminosity	1,490±150[5] L☉
Surface gravity (log g)	0.078±0.027[6] cgs
Temperature	3,500±250[6] K
Age	10[6] Gyr
Other designations
L2 Puppis, L02 Pup, HR 2748, CD−44°3227, HD 56096, LTT 2769, SAO 218549, HIP 34922
Database references
SIMBAD	data

History

SPHERE and VLT NACO image of the nebulosity forming around L₂ Puppis
(Credit: ESO/P. Kervella)

The designation L₂ has a tangled history. This star and another (OU Puppis) were both labelled with "L" by Nicolas-Louis de Lacaille when he created the constellation Puppis within Argo Navis.^[7] The two stars were labelled as "1.L" and "2.L" by Johann Elert Bode in his star catalogue published in 1801.^[8] Later authors used L1 and L2, usually with numeric subscripts (i.e. L₁ and L₂),^[9] but occasionally as superscripts.^[10] The subscripted designation is now universally used where typography allows for subscripts.^[6][11]

L₂ Puppis was discovered to be variable by Benjamin Apthorp Gould in 1872,^[12] and was listed in Uranometria Argentina as 73 G. Puppis with magnitude 5.10v. It has never been given a formal variable star designation, unlike L₁ Puppis which is OU Puppis.^[13]

Variability

A light curve for L₂ Puppis, plotted from Hipparcos data^[14]

L₂ Puppis varies in apparent magnitude by about two magnitudes with a period of 140 days. The average brightness also varies slowly over several years so that the total range is given as magnitude 2.6–6.0. Since 1995 the average brightness has dropped so that the 140-day variations are now between about magnitude 6 and 8.^[4][15] The variation in light may be caused by a combination of radial pulsations in the star's atmosphere and by dimming from circumstellar dust.^[16]

Characteristics

L₂ Puppis is most likely a red-giant branch star that has passed through the main sequence and is evolving to become a white dwarf.^[5] It is shedding mass at the rate of about 5×10⁻⁷ M_☉ per year, forming a circumstellar dust disk and bipolar plumes of gas that are thought to be the start of a "butterfly"-type planetary nebula.^[6]

It has been calculated that the mass of L₂ Puppis is currently about 0.66 M_☉ and its original mass was close to one M_☉ about 10 billion years ago.^[6] Other calculations give higher masses, for example 2+1
−0.5 M_☉, and younger ages such as 1.5 billion years.^[11]

L₂ Puppis has a wide companion, a low-mass red dwarf separated by a minimum of 2,100 astronomical units.^[17] It also has a visual 12th-magnitude companion,^[18] but it is actually a much more distant star not related to this system.^[19] A hundred years ago, they were separated by about a minute of arc, but different proper motions mean that this is now about 1.5′.^[18]

Candidate planet

A candidate exoplanet has been found orbiting L₂ Puppis every 4.69 years at a distance of 2.43 AU. The mass is highly uncertain, at 12 ± 16 M_J, and it might just be a dense clump of gas and dust.^[6]