DD Microscopii
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Microscopium |
| Right ascension | 21h 00m 06.3576s |
| Declination | −42° 38′ 44.9350″ |
| Apparent magnitude (V) | 11.0 - 11.7 |
| Characteristics | |
| Spectral type | K2 III or K5/M0 IIIe |
| U−B color index | +0.37 |
| B−V color index | +1.57 |
| Variable type | Z And |
| Astrometry | |
| Proper motion (μ) | RA: −10.080 mas/yr Dec.: −2.035 mas/yr |
| Parallax (π) | 0.1072±0.0205 mas |
| Distance | 1-2,000 pc |
| Orbit | |
| 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 M☉ |
| Radius | 103 R☉ |
| Surface gravity (log g) | 0.25 cgs |
| Temperature | 3,941 K |
| Metallicity [Fe/H] | −0.93±0.06 dex |
| Rotational velocity (v sin i) | <3 km/s |
| Other designations | |
| DD Mic, CD−43°14304, GSC 07973-00869 | |
| Database references | |
| SIMBAD | data |
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, 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, although parallax measurements place the system at a distance of around 30,000 light years.
It is a symbiotic star system composed of an orange giant with a class of either K2 III or K5/M0 IIIe. 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. The giant star and white dwarf both take about 4 years to orbit each other.
The primary has an enlarged radius of 103 R☉ and an effective temperature of 3,941 K, giving a red hue when viewed through a telescope. DD Microscopii is extremely metal deficient, with an iron abundance only 12% of the Sun, and spins leisurely with a projected rotational velocity lower than 3 km/s. The star system has its origin in the galactic halo of the Milky Way as indicated by the high galactic latitude. 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.