Lambda Andromedae

Lambda Andromedae

Template:Location mark Location of λ Andromedae (circled)
Observation data Epoch J2000      Equinox J2000
Constellation	Andromeda
Right ascension	Template:RA
Declination	Template:DEC
Apparent magnitude (V)	3.65 - 4.05
Characteristics
Evolutionary stage	subgiant
Spectral type	G8 IV
U−B Template:Engvar	+0.688
B−V Template:Engvar	+0.996
Variable type	RS CVn
Astrometry
Radial velocity (Rv)	+6.8 km/s
Proper motion (μ)	RA: Template:Val mas/yr Dec.: Template:Val mas/yr
Parallax (π)	38.5736±0.1179 mas
Distance	Template:Rnd ± Template:Rnd ly (Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)	1.91
Orbit
Primary	A
Companion	B
Period (P)	Template:Val days
Semi-major axis (a)	Template:Val
Eccentricity (e)	Template:Val
Periastron epoch (T)	Template:Val
Argument of periastron (ω) (primary)	Template:Val°
Semi-amplitude (K1) (primary)	Template:Val km/s
Details
A
Mass	Template:Val Template:Solar mass
Radius	Template:Val Template:Solar radius
Luminosity	28.8 Template:Solar luminosity
Surface gravity (log g)	Template:Val cgs
Temperature	Template:Val K
Metallicity [Fe/H]	−0.56 dex
Rotation	Template:Val days
Rotational velocity (v sin i)	7.3 km/s
B
Mass	Template:Val Template:Solar mass
Metallicity [Fe/H]	{{{metal_fe2}}} dex
Other designations
Template:Odlist
Database references
SIMBAD	data

Lambda Andromedae, Latinized from λ Andromedae, also named Udkadua, is a binary star system in the northern constellation of Andromeda. At an estimated distance of approximately Template:Convert from Earth, it has an apparent visual magnitude of around +3.8. This is bright enough to be seen with the naked eye. The system is drifting further away from the Sun with a radial velocity of +6.8 km/s.

Naming

File:Lambda Andromedae.jpg

λ Andromedae in optical light

This star represented the heel of the ancient Sumerian constellation Udkadua, "the storm demon with the gaping mouth". The IAU Working Group on Star Names approved the name Udkadua for this star on 8 May 2025 and it is now so entered in the IAU Catalog of Star Names.

In traditional Arabic astronomy, the stars ι Andromedae, κ Andromedae, and λ Andromedae were known as Kaff al-Musalsala, the hand of the chained woman (i.e. Andromeda), and as Ra’s al-Nāqa, the head of the she-camel.

In Chinese, (), meaning Flying Serpent, refers to an asterism consisting of λ Andromedae, α Lacertae, 4 Lacertae, π² Cygni, π¹ Cygni, HD 206267, ε Cephei, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, the Chinese name for λ Andromedae itself is (, Template:Langx).

Properties

File:LambdaAndLightCurve.png

A light curve for Lambda Andromedae, plotted from Hipparcos data

Lambda Andromedae is a single-lined spectroscopic binary with an orbital period of 20.52 days. The spectrum of the primary matches a stellar classification of G8 IV, meaning that it is an evolved star that is in the subgiant stage. The mass of this star is about 50% larger than that of the Sun, but it has expanded to around seven times the Sun's radius. It is radiating over 28 times the luminosity of the Sun from its outer envelope at an effective temperature of 4,800 K, giving it the characteristic yellow hue of a G-type star.

This is an RS Canum Venaticorum variable and its brightness varies by 0.225 magnitudes, reaching a maximum of 3.70, with a period of 53.952 days. Such variability is theorized to occur because of tidal friction, which results in chromospheric activity. However, the orbit of this system is nearly circular, so the cause of this system's variability remains uncertain. The X-ray luminosity of this star, as measured by the ROSAT satellite, is Template:Val. A magnetic field with an average strength of Template:Val has been detected on this star, which is stronger than the field on the Sun. Starspots on the star's surface have been resolved with Doppler imaging.

The secondary has a very low mass of about Template:Solar mass. It is most likely an L-type brown dwarf.

Evolution

Many different spectral classes have been published for λ Andromedae, ranging from G6 to K1. Most sources give a luminosity class of III (giant) or IV (subgiant). Analysis of the physical properties of the star, including its temperature, luminosity, magnetic field, and stellar wind, show that it has recently experienced the first dredge-up and has begun to ascend the red giant branch although it still has a hot corona and is classified as a subgiant by some definitions.

External links

• http://www.alcyone-software.com/cgi-bin/search.pl?object=HR8961 Template:Webarchive
• Image Lambda Andromedae