SS Cygni

Henry Draper Catalog	HD 206697 [1]
2MASS catalog	2MASS J21424280 + 4335098 [2]
Other names	1RXS J214242.6 + 433506, AAVSO 2138 + 43, BD + 42 4189, HV 84, IOMC 3196000059, X 21407 + 433, V * SS Cyg, GEN # +1.00206697, RE J2142 + 433, WEB 19362, 3A 2140 + 433 , 1H 2140 + 433, RE J214241 + 433511, BM83 X2140 + 433, ALS 11959

SS Cygni also SS Cyg was discovered by Louisa D. Wells in 1896. It is a dwarf nova , and thus a cataclysmically changeable binary star system , in the constellation Swan , consisting of a white dwarf with about 0.6 M _☉ , which isorbitedby a companion with only 0.4 M_☉ .

In terms of structure and composition, the system is similar to the subtypes U Geminorum , SU Ursae Majoris and Z Camelopardalis and forms the prototype of a subclass of dwarf novae, which only show normal outbreaks.

The brightness usually increases every seven to eight weeks for a period of up to two days from 12 ^m to 8 ^m . The northern declination of SS Cygni (about 44 ° N) makes the binary star system from European and North American latitudes almost circumpolar , allowing a large portion of the world's amateur astronomers to monitor behavior. Since the double star lies against the background of the Milky Way, the field of view of the telescope around SS Cygni contains an abundance of useful brightness comparison stars.

The orbit of the system was calculated to be about 50 °. Further studies suggest that the two stars in the SS Cygni system are only about 161,000 km or less apart (from surface to surface). As a result, their orbital period is a little over 6.5 hours.

Astronomically, SS Cygni is also quite close to Earth. Originally believed to be 90 to 100 light years, the distance was changed to about 400 light years in 1952. The 2007 Hubble Space Telescope data was about 540 light years apart, although that value caused difficulties with the theory of dwarf novae. This was in the 2010 to 2012 using radio interferometry with VLBI checked, resulting in a shorter distance of (114 ± 2) pc , respectively (371.6 ± 6.5) Lj yielded. This result is much closer to the old 400 light-year value and also eliminates the problems the larger HST distance made for the theory of dwarf novae.

history

Edward Charles Pickering first announced the discovery of "a (variable) star in the constellation Swan" in Circular No. 12 of the Harvard College Observatory on November 12, 1896. A brightness of 7.2 ^m to 11.2 ^m was photographically recorded over a period of 40 days , which Pickering described as "an unusually large area for cataclysmic variables with such a short period". This new star was named SS Cygni in 1897.

After the discovery of U Geminorum in 1855, SS Cygni was only the second star to be classified in the star class of dwarf novae (today over 375 dwarf novae are known). In the HCO's annual report on September 30, 1896 , Pickering stated that one of his associates "Louisa D. Wells found five new variables from comparing graphs. The most important of these is W Delphini , an Algol-class star ."

After over 100 years of intensive observation, the behavior of SS Cygni in the visual part of the spectrum could be described well. The rest phase determines approx. 75% of the observation times. From this state - known as the spectroscopic low state - the star begins to brighten without warning and reaches its maximum brightness in just one day. The light curve then shows a distribution of alternating wide and narrow eruptions that do not show any particular cyclical pattern. A recurrence of these outbreaks lasting 7 to 14 days can be expected every 4 to 10 weeks.

construction

In this system, the cool, low-mass main sequence star is so close to the white dwarf that a mass transfer takes place through the inner Lagrange point to an accretion disk . It is believed that the outbreaks observed are due to processes occurring in the hydrogen-rich accretion disk. As with SU Ursae Majoris , it is still unclear whether the eruption activity is the result of a sudden transfer of mass (as suggested in the Mass-Transfer Burst Model ) or whether it is instabilities within the accretion disk (as postulated by the Disc Instability Model ) . During an outbreak lasting 10 to 1,000 days, the brightness of typical dwarf novae can increase by 2 to 6 orders of magnitude.

A feature of the light curves of dwarf novae is that new bursts do not necessarily look like previous ones. That said, the shape of the outbreak can change from cycle to cycle. A look at the light curve of SS Cygni shows again and again changing intervals of wide and narrow eruptions with a duration of 18 and 8 days. In addition, infrequent anomalous bursts with a slow rate of rise and a broad and symmetrical light curve are also occasionally observed. Because the system has had this changing eruption characteristic since its discovery, it was an interesting finding that SS Cygni showed no such behavior between 1907 and 1908 and was subject to only minor fluctuations. Such an occurrence could then no longer be observed.

Outbreak types

After a comprehensive study of SS Cygni's light curve, Leon Campbell came to the conclusion in 1934 that the outbreaks can be classified by a sequence of letters depending on their rise and fall times. Class A with a rapid increase to the maximum; Class B with a slightly slower increase; Class C with moderate increase; and class D with an extremely slow increase. The C and D classifications are said to be abnormal compared to the rapid rise in A and B types. However, the A and B outbreaks are then divided into wide and narrow outbreaks. Further research showed that class A leads with 64% of outbreaks of this type, B with 9%, C with 18% and D with 9%. A later study by Bath and van Paradijs in 1983 refined the definitions of classes so that type A outbreaks generally start from a resting state with a visual size of (11.9 ± 0.12) ^m , while the others start from (11, 64 ± 0.30) ^m brighten.

Statistical studies of the light curve of SS Cygni over the years have shown numerous correlations, of which the alternating occurrence of wide and narrow outbreaks is particularly prominent. A study of the long-term behavior of SS Cygni was carried out by Cannizzo and Mattei in 1992 regarding the type of outbreak. This publication assumes that a breakout occurs when the system exceeds a visual size of 10 ^meters . The eruptions are then separated by a time scale of long or broad eruptions (denoted by the letter "L") and lasting more than 12 days. The short or narrow bursts (denoted by the letter "S") last less than 12 days. A data analysis revealed the most common sequence as LS (with 134 occurrences), LLS (69), LSSS (14) and LLSS (8). Together, these sequences made up 89% of the events examined.

Causes of the outbreak

It has been suggested that the determining factor in whether an eruption will have a wide or a narrow characteristic depends on the amount of mass present in the accretion disk at the onset of thermal instability. That is, the narrow outbreak could be due to a medium mass transfer, while wide outbreaks could indicate a large mass transfer (≥ 1.1 × 10 ⁻⁸ M _☉ / year).

The light seen in the visible part of the spectrum during an outbreak comes from the cooler outermost area of the accretion disk. However, the inner disc is hotter due to the released accretion energy and is therefore a source of ultraviolet radiation emissions . The boundary layer between the accretion disc and the white dwarf is even hotter and therefore emits X-rays and ultraviolet radiation. In order to study the properties of the inner regions of the disk and the boundary layer of SS Cygni and other dwarf novae types, observations with satellites are necessary, the instruments of which can record in high-energy bands.

Individual evidence

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j SS Cyg. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed on May 8, 2019 .
↑ ^a ^b ^c ^d ^e ^f SS Cyg. In: VSX. AAVSO , accessed May 8, 2019 .
↑ ^a ^b ^c Honey, WB, et al .: Quiescent and outburst photometry of the dwarf nova SS Cygni . In: MNRAS (ISSN 0035-8711), vol. 236, Feb. 1, 1989, p. 727-734. . February 1989. bibcode : 1989MNRAS.236..727H . doi : 10.1093 / mnras / 236.4.727 .
↑ ^a ^b Schreiber, MR, et al .: The dwarf nova SS Cygni: what is wrong? . In: Astronomy and Astrophysics, Volume 473, Issue 3, October III 2007, pp.897-901 . October 2007. bibcode : 2007A & A ... 473..897S . doi : 10.1051 / 0004-6361: 20078146 .
↑ JCA Miller-Jones, et al .: An accurate geometric distance to the compact binary SS Cygni vindicates accretion disc theory . In: Science, May 24, 2013, Vol. 340, No. 6135, pp. 950-952 . May 24, 2013. arxiv : 1305.5846 . doi : 10.1126 / science.1237145 .
↑ ^a ^b ^c Kerri Malatesta: SS Cygni . In: Variable Star of the Month . April 13, 2010.
↑ Hazen, Martha: The Centennial of the Discovery of SS Cygni . In: The Journal of the American Association of Variable Star Observers, vol. 26, no. 1, p. 59-61 . 1997. bibcode : 1997JAVSO..26 ... 59H .
↑ Campbell, Leon; Shapley, Harlow: The light curve of SS Cygni, 213843 . In: Annals of the Astronomical Observatory of Harvard College; v. 90, no. 3, Cambridge, Mass .: The Observatory, 1940., p. 93-162 . 1940. bibcode : 1940AnHar..90 ... 93C .
^ ^A ^b G. T. Bath & J. van Paradijs: Outburst period-energy relations in cataclysmic novae . In: Naturevolume 305, pages 33-36 (1983) . 1983. doi : 10.1038 / 305033a0 .
↑ Sterne, Theodore E., et al .: Properties of the light curve of SS Cygni . In: Annals of the Astronomical Observatory of Harvard College; v. 90, no. 6, Cambridge, Mass .: The Observatory, 1940., p. 189-206 . 1940. bibcode : 1940AnHar..90..189S .
↑ Cannizzo, John K., et al .: On the long-term behavior of SS Cygni . In: Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 401, no. 2, p. 642-653 . December 1992. bibcode : 1992ApJ ... 401..642C . doi : 10.1086 / 172092 .
↑ Cannizzo, John K., 1993: The Accretion Disk Limit Cycle Model: Toward an Understanding of the Long-Term Behavior of SS Cygni . In: Astrophysical Journal v.419, p.318 . December 1993. bibcode : 1993ApJ ... 419..318C . doi : 10.1086 / 173486 .

[Simbad-1] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j SS Cyg. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed on May 8, 2019 .

[VSXEntry-2] ↑ ^a ^b ^c ^d ^e ^f SS Cyg. In: VSX. AAVSO , accessed May 8, 2019 .

[Honey,_et_al.-3] Honey, WB, et al .: Quiescent and outburst photometry of the dwarf nova SS Cygni . In: MNRAS (ISSN 0035-8711), vol. 236, Feb. 1, 1989, p. 727-734. . February 1989. bibcode : 1989MNRAS.236..727H . doi : 10.1093 / mnras / 236.4.727 .

[Schreiber,_M._R.,_et_al.-4] Schreiber, MR, et al .: The dwarf nova SS Cygni: what is wrong? . In: Astronomy and Astrophysics, Volume 473, Issue 3, October III 2007, pp.897-901 . October 2007. bibcode : 2007A & A ... 473..897S . doi : 10.1051 / 0004-6361: 20078146 .

[J._C._A._Miller-Jones,_et_al.-5] JCA Miller-Jones, et al .: An accurate geometric distance to the compact binary SS Cygni vindicates accretion disc theory . In: Science, May 24, 2013, Vol. 340, No. 6135, pp. 950-952 . May 24, 2013. arxiv : 1305.5846 . doi : 10.1126 / science.1237145 .

[Kerri_Malatesta-6] Kerri Malatesta: SS Cygni . In: Variable Star of the Month . April 13, 2010.

[Hazen,_Martha-7] Hazen, Martha: The Centennial of the Discovery of SS Cygni . In: The Journal of the American Association of Variable Star Observers, vol. 26, no. 1, p. 59-61 . 1997. bibcode : 1997JAVSO..26 ... 59H .

[Campbell,_Leon,_1940-8] Campbell, Leon; Shapley, Harlow: The light curve of SS Cygni, 213843 . In: Annals of the Astronomical Observatory of Harvard College; v. 90, no. 3, Cambridge, Mass .: The Observatory, 1940., p. 93-162 . 1940. bibcode : 1940AnHar..90 ... 93C .

[G._T._Bath,_et_al.-9] A ^b G. T. Bath & J. van Paradijs: Outburst period-energy relations in cataclysmic novae . In: Naturevolume 305, pages 33-36 (1983) . 1983. doi : 10.1038 / 305033a0 .

[Sterne,_Theodore_E.,_et_al.-10] Sterne, Theodore E., et al .: Properties of the light curve of SS Cygni . In: Annals of the Astronomical Observatory of Harvard College; v. 90, no. 6, Cambridge, Mass .: The Observatory, 1940., p. 189-206 . 1940. bibcode : 1940AnHar..90..189S .

[Cannizzo,_John_K.,_et_al.-11] Cannizzo, John K., et al .: On the long-term behavior of SS Cygni . In: Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 401, no. 2, p. 642-653 . December 1992. bibcode : 1992ApJ ... 401..642C . doi : 10.1086 / 172092 .

[Cannizzo,_John_K.,_1993-12] Cannizzo, John K., 1993: The Accretion Disk Limit Cycle Model: Toward an Understanding of the Long-Term Behavior of SS Cygni . In: Astrophysical Journal v.419, p.318 . December 1993. bibcode : 1993ApJ ... 419..318C . doi : 10.1086 / 173486 .