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]
Distance1-2,000[4] pc
Orbit[7]
Primaryyellow giant
CompanionWhite 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
Mass1.45[8] M☉
Radius103[9] R☉
Surface gravity (log g)0.25[8] cgs
Temperature3,941[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
SIMBADdata

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. 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]

References
  1. "ASAS-SN Variable Stars Database". ASAS-SN Variable Stars Database. ASAS-SN. Retrieved 28 November 2022.
  2. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  3. Samus’, N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (January 2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80–88. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. ISSN 1063-7729. S2CID 125853869.
  4. Pereira, C.B.; Roig, F. (2009). "High-Resolution Spectroscopic Observations of Four Yellow-Type Symbiotic Stars: CD-43°14304, Hen 3-1213, Hen 3-863, and StHα 176". The Astronomical Journal. 137 (1): 118–28. Bibcode:2009AJ....137..118P. doi:10.1088/0004-6256/137/1/118.
  5. Schulte-Ladbeck, R. E. (January 1988). "Near-infrared spectral classification of symbiotic stars". Astronomy and Astrophysics. 189: 97–108. Bibcode:1988A&A...189...97S. ISSN 0004-6361.
  6. Munari, U.; Yudin, B. F.; Taranova, O. G.; Massone, G.; Marang, F.; Roberts, G.; Winkler, H.; Whitelock, P. A. (May 1992). "UBVRI-JHKL photometric catalogue of symbiotic stars". Astronomy and Astrophysics Supplement Series. 93: 383–390. Bibcode:1992A&AS...93..383M. ISSN 0365-0138.
  7. Schmid, H. M.; Dumm, T.; Murset, U.; Nussbaumer, H.; Schild, H.; Schmutz, W. (January 1998). "High resolution spectroscopy of symbiotic stars. III. Radial velocity curve for CD--43(deg) 14304". Astronomy and Astrophysics. 329: 986–990. Bibcode:1998A&A...329..986S. ISSN 0004-6361.
  8. Anders, F.; et al. (February 2022). "Photo-astrometric distances, extinctions, and astrophysical parameters for Gaia EDR3 stars brighter than G = 18.5". Astronomy & Astrophysics. 658: A91. arXiv:2111.01860. Bibcode:2022A&A...658A..91A. doi:10.1051/0004-6361/202142369. eISSN 1432-0746. ISSN 0004-6361.
  9. Stassun, Keivan G.; et al. (9 September 2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467. ISSN 0004-6256.
  10. Gałan, Cezary; Mikołajewska, Joanna; Hinkle, Kenneth H.; Joyce, Richard R. (15 December 2016). "Chemical abundance analysis of 13 southern symbiotic giants from high-resolution spectra at ~1.56 μm". Monthly Notices of the Royal Astronomical Society. 466 (2): 2194–2201. arXiv:1612.04632. Bibcode:2017MNRAS.466.2194G. doi:10.1093/mnras/stw3266. eISSN 1365-2966. ISSN 0035-8711.
  11. "DD Mic". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved March 25, 2015.
  12. Kazarovets, E. V.; Samus, N. N.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (August 2006). "The 78th Name-List of Variable Stars". Information Bulletin on Variable Stars. 5721: 1. Bibcode:2006IBVS.5721....1K. ISSN 0374-0676.
  13. Watson, C. L.; Henden, A. A.; Price, A. (May 2006). "The International Variable Star Index (VSX)". Society for Astronomical Sciences Annual Symposium. 25: 47. Bibcode:2006SASS...25...47W.
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