SY Cancri

SY Cancri

SY Cancri is part of the Beehive Cluster
Observation data Epoch J2000.0       Equinox J2000.0
Constellation	Cancer
Right ascension	09h 01m 03.320s [1]
Declination	+17° 53′ 56.03″ [1]
Apparent magnitude  (V)	10.5 - 14.5 [2]
Characteristics
Evolutionary stage	White dwarf + Red dwarf
Spectral type	WD + G8±2 V [3]
Variable type	U Gem [2]
Astrometry
Proper motion (μ)	RA: −29.138 mas/yr [1] Dec.: −6.423 mas/yr [1]
Parallax (π)	2.461±0.0253  mas [1]
Distance	1,330 ± 10  ly (406 ± 4  pc)
Orbit [3]
Period (P)	9.17701 h
Periastron epoch (T)	2451300.254±0.002  HJD
Semi-amplitude (K2) (secondary)	88.0±2.9 km/s
Details [3]
Primary
Mass	0.77–1.54  M☉
Secondary
Mass	0.65−1.31  M☉
Other designations
SY Cnc, AAVSO 0855+18, BD+18°2101, TIC 437056841 [4]
Database references
SIMBAD	data

SY Cancri (SY Cnc) is a binary star system located in the northern constellation of Cancer and is part of the Beehive Cluster. It is a cataclysmic variable (CV) of the Z Cam type and is the third brightest Z Cam star to be discovered. The system consists of a white dwarf primary accreting material from a low-mass secondary companion, exhibiting periodic outbursts due to instabilities in the accretion disk. The system is notable for its relatively infrequent "standstills", periods of stable intermediate brightness between normal and outbursts. ^[5]

Discovery and observations

The variability of this system was discovered by L. Ceraski, and was reported in 1929 by S. Blažko. Between 1912 and 1928, Ceraski found it varied in brightness from magnitude 9.5 and 12.5. A follow up study in 1931 by R. Prager reported the brightness ranging from magnitude 9.9 to below 12. ^[5] In 1950, G. Herbig performed a spectroscopic study, finding a spectrum similar to the cataclysmic variable Z Camelopardalis. ^[6] Multicolor photometry has been collected over decades, revealing patterns of outbursts and rapid flickering. ^[7] In 2009, spectroscopic analysis suggested unstable mass transfer, with a high mass ratio for the system. ^[8]

In 2024, a bow-shock nebula was discovered around SY Cnc through amateur imaging from the Southern Hα Sky Survey Atlas (SHASSA), marking it as only the second such feature known in a Z Cam dwarf nova. ^[5]

Nebula

SY Cnc is associated with a faint bow-shock nebula (PaEl 1), discovered in 2024, spanning ∼3 arcminutes in diameter with bipolar, conical geometry. The nebula features a parabolic rim prominent in O III and Hα emission, formed by the system's supersonic wind (transverse velocity 56.8 ± 0.6 km/s) interacting with the interstellar medium. SY Cnc lies near the western edge of a larger ∼30′ (∼1.8 pc) Hα-emitting nebula, suggesting possible past nova ejecta (∼7800 years ago) or photoionization by the CV. This feature implies such nebulae may be more common in Z Cam systems than previously recognized. Another system with similar properties is V341 Ara. ^[5]

References

1. Vallenari, A.; et al. (Gaia collaboration) (2023), "Gaia Data Release 3. Summary of the content and survey properties", Astronomy and Astrophysics, 674: A1, arXiv: 2208.00211 , Bibcode:2023A&A...674A...1G, doi: 10.1051/0004-6361/202243940 , S2CID   244398875. Gaia DR3 record for this source at VizieR .
2. Samus, N. N.; et al. (2017), "General Catalogue of Variable Stars", Astronomy Reports, GCVS 5.1, 61 (1): 80–88, Bibcode:2017ARep...61...80S, doi:10.1134/S1063772917010085, S2CID   255195566.
3. Casares, J.; et al. (November 2009), "SY Cnc, a case for unstable mass transfer?", Monthly Notices of the Royal Astronomical Society, 399 (3): 1534–1538, arXiv: 0907.4432 , Bibcode:2009MNRAS.399.1534C, doi:10.1111/j.1365-2966.2009.15384.x.
4. "SY Cnc", SIMBAD , Centre de données astronomiques de Strasbourg , retrieved 2025-11-29.
5. Bond, Howard E.; et al. (December 2024), "Discovery of a Bow-shock Nebula Around the Z Cam-type Cataclysmic Variable SY Cancri", The Astronomical Journal, 168 (6), id. 249, arXiv: 2409.06835 , Bibcode:2024AJ....168..249B, doi: 10.3847/1538-3881/ad7a71 .
6. Herbig, George H. (October 1950), "The Spectra of Five Irregular Variable Stars", Publications of the Astronomical Society of the Pacific, 62 (367): 211, Bibcode:1950PASP...62..211H, doi:10.1086/126276.
7. Landolt, A. U.; Clem, J. L. (June 2018). "The Dwarf Nova SY Cancri and its Environs". Journal of the American Association of Variable Star Observers (JAAVSO). 46 (1): 50. Bibcode:2018JAVSO..46...50L. ISSN   0271-9053.
8. Casares, J.; Martinez-Pais, I. G.; Rodriguez-Gil, P. (2009-07-27). "SY CNC, a case for unstable mass transfer?". Monthly Notices of the Royal Astronomical Society. 399 (3): 1534–1538. arXiv: 0907.4432 . Bibcode:2009MNRAS.399.1534C. doi: 10.1111/j.1365-2966.2009.15384.x .

Further reading

• Smith, Robert Connon; et al. (June 2005), "A non-main-sequence secondary in SY Cancri", Monthly Notices of the Royal Astronomical Society, 360 (1): 364–374, arXiv: astro-ph/0506075 , Bibcode:2005MNRAS.360..364S, doi:10.1111/j.1365-2966.2005.09040.x.
• Pezzuto, S.; et al. (April 1992), "Rapid oscillations in the dwarf novae SY Cancri, YZ Cancri and AH Herculis", Astronomy and Astrophysics, 257: 523–530, Bibcode:1992A&A...257..523P.
• Middleditch, J.; Cordova, F. A. (April 1982), "The colors of the pulsations and flickering of SY CNC during outburst", Astrophysical Journal, 255: 585–595, Bibcode:1982ApJ...255..585M, doi:10.1086/159860.