Astronomy:AZ Cancri

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Short description: Star in the constellation Cancer
AZ Cancri
AZCnc.jpeg
Image of AZ Cancri from the Sloan Digital Sky Survey; it is the red star close to the centre.
Observation data
Equinox J2000.0]] (ICRS)
Constellation Cancer
Right ascension  08h 40m 29.679s[1]
Declination +18° 24′ 08.73″[1]
Apparent magnitude (V) 17.59[2]
Characteristics
Spectral type M6.5eV[2]
B−V color index 1.6[2]
V−R color index 1.0[2]
R−I color index 3.2[2]
Variable type UV[3]
Astrometry
Proper motion (μ) RA: −809.817[1] mas/yr
Dec.: −448.969[1] mas/yr
Parallax (π)73.8573 ± 0.0671[1] mas
Distance44.16 ± 0.04 ly
(13.54 ± 0.01 pc)
Absolute magnitude (MV)16.85[4]
Details
Mass0.10[5] M☉
Radius0.13[5] R☉
Luminosity0.015[5] L☉
Surface gravity (log g)5.24[6] cgs
Temperature2,825[5] K
Metallicity [Fe/H]+0.27[7] dex
Age100[8] Myr
Other designations
AZ Cnc, GJ 316.1, LHS 2034, NLTT 20016[2]
Database references
SIMBADdata

AZ Cancri (AZ Cnc) is a M-type flare star in the constellation Cancer.[2] It has an apparent visual magnitude of approximately 17.59.[2]

Observations

AZ Cancri is a member of the Beehive Cluster, also known as Praesepe or NGC 2632. The spectral type of AZ Cnc is M6e,[9] specifically M6.5Ve,[10] and was catalogued as a flare star by Haro and Chavira in 1964 (called by them T4).[11][12] AZ Cnc has also been found to be an x-ray source, with the ROSAT designations of RX J0840.4+1824 and 1RXS J084029.9+182417. The X-ray luminosity has been found to be 27.40 ergs/s[13]

Physical characteristics

The absolute magnitude of the star has been found to be 16.9, and thus its luminosity is approximately 3.020 x 1030 ergs/s.[citation needed]

AZ Cancri is located approximately 14.0 parsecs (46 ly) from the Sun, and is considered a very low-mass star[14] with a radial velocity of 64.2±0.6 km/s.[15] AZ Cancri belongs kinematically to the old disk.[15] It is rotating at approximately 7.9±2.8 km/s.[15]

Flaring

A red band light curve for a flare on AZ Cancri, adapted from Fuhrmeister et al. (2005)[15]

The X-ray luminosity of AZ Cnc increased by at least two orders of magnitude during a flare that lasted more than 3 hours and reached a peak emission level of more than 1029 ergs/s.[13] During another long duration flare (March 14, 2002) on AZ Cnc, very strong wing asymmetries occurred in all lines of the Balmer series and all strong He I lines, but not in the metal lines.[15]

The flaring atmosphere of AZ Cancri has been analysed with a stellar atmosphere model,[16][15] and was found to consist of

  1. an underlying photosphere,
  2. a linear temperature rise vs. log column mass in the chromosphere, and
  3. transition region (TR) with different gradients.[15]

For the underlying photosphere, the effective temperature was found to be 2800 K, and a solar chemical composition was used.[15] The last spectrum taken in the series after the flare was used for the quiescent chromosphere.[15]

The line asymmetries have been attributed to downward moving material,[15] specifically a series of flare-triggered downward moving chromospheric condensations, or chromospheric downward condensations (CDC)s as on the Sun.[17]

Theory of coronal heating

The electrodynamic coupling theory of coronal heating developed in a solar context,[18] has been applied to stellar corona.[19] A distinctive feature is the occurrence of a resonance between the convective turnover time and the crossing time for Alfvén waves in a coronal loop. The resonance attains a maximum among the early M dwarf spectral types and declines thereafter. A turnover in coronal heating efficiency, presumably manifested by a decrease in Lx/Lbol, becomes evident toward the late M spectral types when the theory is applicable. This is consistent with an apparent lack of X-ray emission among the late M dwarfs.[20] Coronal heating efficiencies do not decrease toward the presumably totally convective stars near the end of the main sequence.[13] For "saturated" M dwarfs, 0.1% of all energy is typically radiated in X-rays, while for AZ Cnc this number increases during flaring to 7%.[13] So far there is no evidence to suggest that AZ Cnc is less efficient than more massive dwarfs in creating a corona.[13] The saturation boundary in X-ray luminosity extends to late M dwarfs, with Lx/Lbol ~ 10−3 for saturated dwarfs outside flaring. No coronal dividing line exists in the Hertzsprung–Russell diagram at the low-mass end of the main sequence.[13]

AZ Cnc casts doubt on the applicability of electrodynamic coupling as there is no evidence for a sharp drop in Lx/Lbol when compared with other late M stars at least until subtype M8.[13]

Dynamo

AZ Cnc has a corona and this may indicate that a distributive dynamo is just as efficient in producing magnetic flux as a shell dynamo.[13] Between the generation of a magnetic field and the emission of X-rays lies the coronal heating mechanism.[13]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 "V* AZ Cnc". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=V%2A+AZ+Cnc. 
  3. ↑ AZ Cnc, database entry, The combined table of GCVS Vols I-III and NL 67-78 with improved coordinates, General Catalogue of Variable Stars , Sternberg Astronomical Institute, Moscow, Russia. Accessed on line October 13, 2010.
  4. ↑ From apparent magnitude and parallax.
  5. ↑ 5.0 5.1 5.2 5.3 Sebastian, D.; Gillon, M.; Ducrot, E.; Pozuelos, F. J.; Garcia, L. J.; Günther, M. N.; Delrez, L.; Queloz, D. et al. (2021). "SPECULOOS: Ultracool dwarf transit survey. Target list and strategy". Astronomy and Astrophysics 645: 645. doi:10.1051/0004-6361/202038827. Bibcode: 2021A&A...645A.100S. 
  6. ↑ Stassun, Keivan G. et al. (9 September 2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal 158 (4): 138. doi:10.3847/1538-3881/ab3467. Bibcode: 2019AJ....158..138S. 
  7. ↑ Newton, Elisabeth R. et al. (January 2017). "The Hα Emission of Nearby M Dwarfs and its Relation to Stellar Rotation". The Astrophysical Journal 834 (1): 13. doi:10.3847/1538-4357/834/1/85. 85. Bibcode: 2017ApJ...834...85N. 
  8. ↑ Klutsch, A.; Freire Ferrero, R.; Guillout, P.; Frasca, A.; Marilli, E.; Montes, D. (2014). "Reliable probabilistic determination of membership in stellar kinematic groups in the young disk". Astronomy and Astrophysics 567: A52. doi:10.1051/0004-6361/201322575. Bibcode: 2014A&A...567A..52K. 
  9. ↑ Kirkpatrick, J. Davy; Henry, Todd J.; McCarthy, Donald W. Jr. (1991). "A standard stellar spectral sequence in the red/near-infrared - Classes K5 to M9". Astrophysical Journal Supplement 77: 417. doi:10.1086/191611. Bibcode: 1991ApJS...77..417K. 
  10. ↑ Dahn, C.; Green, R.; Keel, W.; Hamilton, D.; Kallarakal, V.; Liebert, James (Sep 1985). "The Absolute Magnitude of the Flare Star AZ Cancri (LHS 2034)". Information Bulletin on Variable Stars 2796 (1): 1–2. Bibcode: 1985IBVS.2796....1D. 
  11. ↑ Bidelman, W. P.; D. Hoffleit (1983). "The Absolute Magnitude of AZ Cancri". Information Bulletin on Variable Stars 2414 (1): 1. Bibcode: 1983IBVS.2414....1B. 
  12. ↑ "Flare stars in the Praesepe field". Bol Inst Tonantzintla. 2 (12): 95–100. Dec 1976. Bibcode: 1976BITon...2...95H. 
  13. ↑ 13.0 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 Fleming TA; Giampapa MS; Schmitt JHMM; Bookbinder JA (Jun 1993). "Stellar coronae at the end of the main sequence - A ROSAT survey of the late M dwarfs". Astrophys. J. 410 (1): 387–92. doi:10.1086/172755. Bibcode: 1993ApJ...410..387F. 
  14. ↑ "U.S. Naval Observatory CCD parallaxes of faint stars. I - Program description and first results". Astron. J. 103: 638. 1992. doi:10.1086/116091. Bibcode: 1992AJ....103..638M. 
  15. ↑ 15.0 15.1 15.2 15.3 15.4 15.5 15.6 15.7 15.8 15.9 Fuhrmeister B; Schmitt JHMM; Hauschildt PH (Jun 2005). "Detection of red line asymmetries in LHS 2034". Astron. Astrophys. 436 (2): 677–86. doi:10.1051/0004-6361:20042518. Bibcode: 2005A&A...436..677F. 
  16. ↑ "The NextGen Model Atmosphere Grid for 3000<=T_eff<=10,000 K". Astrophys. J. 512 (1): 377–85. Feb 1999. doi:10.1086/306745. Bibcode: 1999ApJ...512..377H. 
  17. ↑ Fisher GH (Nov 1989). "Dynamics of flare-driven chromospheric condensations". Astrophys. J. 346 (11): 1019–29. doi:10.1086/168084. Bibcode: 1989ApJ...346.1019F. 
  18. ↑ Ionson J (1984). "A unified theory of electrodynamic coupling in coronal magnetic loops - The coronal heating problem". Astrophys. J. 276: 357. doi:10.1086/161620. Bibcode: 1984ApJ...276..357I. 
  19. ↑ Mullan DJ (1984). "On the possibility of resonant electrodynamic coupling in the coronae of red dwarfs". Astrophys. J. 282: 603. doi:10.1086/162239. Bibcode: 1984ApJ...282..603M. 
  20. ↑ Bookbinder, J. A. (1985). Observations of non-thermal radiation from late-type stars (Thesis). Cambridge, MA: Harvard University. Bibcode:1985PhDT........13B.



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