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]
Image of AZ Cancri from the Sloan Digital Sky Survey; it is the red star close to the centre. | |
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
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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 mas[1] |
Distance | 44.16 ± 0.04 ly (13.54 ± 0.01 pc) |
Absolute magnitude (MV) | 16.85[4] |
Details | |
Mass | 0.10[5] M☉ |
Radius | 0.13[5] R☉ |
Luminosity | 0.015[5] L☉ |
Surface gravity (log g) | 5.24[6] cgs |
Temperature | 2,825[5] K |
Metallicity [Fe/H] | +0.27[7] dex |
Age | 100[8] Myr |
Other designations | |
Database references | |
SIMBAD | data |
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]
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]
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
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]
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]
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]