DD Microscopii

DD Microscopii, also known as CD−43°14304, is a binary star system in the constellation Microscopium. The system has a combined average apparent magnitude around 11,^[12] making it readily visible in telescopes but not to the naked eye. It is thought to be at a distance of one or two thousand parsecs,^[4] although parallax measurements place the system at a distance of around 30,000 light years.^[2]

DD Microscopii

A visual band light curve for DD Microscopii, plotted from ASAS-SN data[1]
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Microscopium
Right ascension	21h 00m 06.3576s[2]
Declination	−42° 38′ 44.9350″[2]
Apparent magnitude (V)	11.0 - 11.7[3]
Characteristics
Spectral type	K2 III[4] or K5/M0 IIIe[5]
U−B color index	+0.37[6]
B−V color index	+1.57[6]
Variable type	Z And[3]
Astrometry
Proper motion (μ)	RA: −10.080 mas/yr[2] Dec.: −2.035 mas/yr[2]
Parallax (π)	0.1072±0.0205 mas[2]
Distance	1-2,000[4] pc
Orbit[7]
Primary	yellow giant
Companion	White dwarf
Period (P)	1,442 d
Eccentricity (e)	0.22
Periastron epoch (T)	2,445,560
Argument of periastron (ω) (primary)	261°
Semi-amplitude (K1) (primary)	4.6 km/s
Details
yellow giant
Mass	1.45[8] M☉
Radius	103[9] R☉
Surface gravity (log g)	0.25[8] cgs
Temperature	3,941[8] K
Metallicity [Fe/H]	−0.93±0.06[10] dex
Rotational velocity (v sin i)	<3[7] km/s
Other designations
DD Mic, CD−43°14304, GSC 07973-00869[11]
Database references
SIMBAD	data

It is a symbiotic star system composed of an orange giant with a class of either K2 III^[4] or K5/M0 IIIe.^[5] Both stellar classifications of the primary indicate a red giant, but one has a regular spectrum while the other shows an evolved star with the characteristics of a K5 and M0 giant star plus emission lines in its spectrum. The secondary is a white dwarf in close orbit, ionizing the stellar wind of the larger star.^{[citation needed]} The giant star and white dwarf both take about 4 years to orbit each other.^[7]

The primary has an enlarged radius of 103 R_☉^[9] and an effective temperature of 3,941 K,^[8] giving a red hue when viewed through a telescope. DD Microscopii is extremely metal deficient, with an iron abundance only 12% of the Sun,^[10] and spins leisurely with a projected rotational velocity lower than 3 km/s.^[7] The star system has its origin in the galactic halo of the Milky Way as indicated by the high galactic latitude.^[4] DD Microscopii is cataloged as a Z Andromedae variable, a type of symbiotic binary with occasional outbursts. It fluctuates between magnitudes 11.0 and 11.7 over a span of almost 400 days.^[13]