EG Andromedae

Short description: Binary star system in the constellation Andromeda

EG Andromedae

View of the Andromeda Galaxy, with EG And circled in red. The star is much closer than Andromeda, within the Milky Way galaxy.

Observation data
Equinox J2000.0]] (ICRS)
Constellation | Andromeda
Right ascension |  00h 44m 37.18738s[1]
Declination | +40° 40′ 45.7048″[1]
Apparent magnitude (V) | 6.97 - 7.80 variable[2]
Characteristics
Spectral type | M2IIIep[2]
Apparent magnitude (U) | 10.54[3]
Apparent magnitude (B) | 8.93[3]
Apparent magnitude (V) | 7.22[3]
Apparent magnitude (G) | 6.29[1]
Apparent magnitude (J) | 3.65[3]
Apparent magnitude (H) | 2.79[3]
Apparent magnitude (K) | 2.56[3]
U−B color index | 3.32[3]
B−V color index | 1.71[3]
Variable type | Symbiotic[2]
Astrometry
Radial velocity (Rv)| −94.80±0.30[4] km/s
Proper motion (μ)|  RA: 8.614[1] mas/yr
Dec.: −15.466[1] mas/yr
Parallax (π)| 1.6452 ± 0.0335[1] mas
Distance| 1,980 ± 40 ly
(610 ± 10 pc)
Orbit
Period (P)| 482.5±1.3 days[5]
Eccentricity (e)| 0[5]
Inclination (i)| 60[6]°
Semi-amplitude (K1)
(primary)| 7.30±0.13[5] km/s
Details
White dwarf
Mass| 0.4[7] M☉
Radius| 1.9–2.3×10−2[6] R☉
Luminosity| 12.9-38.4[6] L☉
Surface gravity (log g)| 7.5[6] cgs
Temperature| 80–95×103[6] K
Donor star
Mass| 1.1 - 2.4[5] M☉
Temperature| 3730±130[5] K
Other designations

2MASS J00443718+4040456, BD+39 167, HD 4174, HIP 3494, SAO 36618, TYC 2801-1704-1

Database references
SIMBAD| data

EG Andromedae (often abbreviated to EG And) is a symbiotic binary in the constellation Andromeda. Its apparent visual magnitude varies between 6.97 and 7.80.[2]

## Contents

* 1 System
* 2 Spectrum
* 3 Variability
* 4 Bow shock of a ghost planetary nebula
* 5 Gallery
* 6 References

## System

The EG Andromedae system hosts a white dwarf and an evolved giant star, with an orbital period of 482.5 days. The giant star is losing mass through its stellar wind at a rate higher than 10−6 M☉/yr, and the white dwarf is accreting a fraction of this mass without forming an accretion disk. The white dwarf itself could emit a hot wind that interacts with the cooler one of the giant star, in addition to inducing the photoionization of the latter.[6] X-ray observations, however, failed to detect emission coming from colliding winds, but established the non-magnetic nature of the white dwarf and estimated its accretion rate at 1–10×10−7 M☉/yr.[7]

The giant star does not fill its Roche lobe but there are still large uncertainties on its mass and radius.[5] Even the parameters of the white dwarf are not strictly constrained, but available models can give lower and upper limits.[6]

## Spectrum

The optical spectral classification of EG Andromedae is M2IIIep,[2] the one of a cool giant star with a peculiar spectrum and strong emission lines. The white dwarf contaminates the spectrum of the giant star photoionizes the stellar wind, giving rise to the spectral peculiarities. Emission lines H-alpha and H-beta, as well as TiO and CaI ones, change in phase with the orbit.[5]

The white dwarf is best studied in the ultraviolet, where also highly ionized species sulfur, oxygen, nitrogen, carbon and phosphorus can be identified with their absorption or emission lines.[6]

X-ray observation of EG Andromedae detected a hot plasma (at a temperature of 3 keV) that is likely situated in the outer boundary layer of the white dwarf, without any contribution from an accretion disk.[7]

## Variability

The visual band light curve of EG Andromedae, adapted from Skopal (2006)[8]

Discovery of the photometric variability of EG Andromedae was announced in 1964 by Polish astronomer Tadeusz Jarzębowski, based on observations made from 1961 through 1963 at Wroclaw Observatory.[9]

To date, no outburst has been observed in EG Andromedae. The observed variability is well described by the two components eclipsing each other during the orbit. However, there is some evidence that the giant star and the wind flow have an intrinsic variation.[10]

## Bow shock of a ghost planetary nebula

Sketch showing the direction of movement with an arrow. EG And is in the center of the ellipse, at the base of the arrow. The blue arc on the lower left is the bow shock SDSO1.[11]

A giant nebula near the Andromeda galaxy (M31) was detected by amateur astronomers in doubly ionized oxygen and was cataloged as the Strottner–Drechsler–Sainty Object (SDSO1). Initially it was suspected to belong to M31, but other scenarios, such as supernova remnant, planetary nebula or stellar bow shock nebula were considered.[12][13] A later study did however find that SDSO1 is located within the Milky Way and it was considered to be a interstellar gas filament.[14] Another study found that EG Andromedae expelled a planetary nebula 400,000 years ago. This planetary nebula faded and is today a ghost planetary nebula (GPN) with a diameter of 20 parsec. EG And has a hypersonic speed of 107 km/s relative to the interstellar medium. Therefore the giant GPN formed the bow shock SDSO1 around it.[11]

## Gallery

* Discovery images of the giant oxygen nebula around M31

* Wide-field image using H-alpha (red), oxygen [OIII] (blue) and a RGB combination.

* Detailed view of part

Detailed view of part of the nebula by the group "Deep Sky Collective"

* Image taken by the amateur astronomer group "Association of Widefield Astrophotographers"

Image taken by the amateur astronomer group "Association of Widefield Astrophotographers"

## 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 EG And, database entry, Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.), N. N. Samus, O. V. Durlevich, et al., CDS ID II/250 Accessed on line 2018-10-17.
3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Database entry, Catalogue of Stellar Photometry in Johnson's 11-color system (2002 Ed.), J. R. Ducati, CDS ID II/237 Accessed on line 2018-10-25.
4. ↑ de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics 546: 14, doi:10.1051/0004-6361/201219219, A61, Bibcode: 2012A&A...546A..61D.
5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 Kenyon, S. J.; Garcia, M. R. (2016). "EG Andromedae: A New Orbit and Additional Evidence for a Photoionized Wind". The Astronomical Journal 152 (1): 1. doi:10.3847/0004-6256/152/1/1. Bibcode: 2016AJ....152....1K.
6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 Sion, E. M.; Godon, P.; Mikolajewska, J.; Sabra, B.; Kolobow, C. (2017). "FUSE Spectroscopy of the Accreting Hot Components in Symbiotic Variables". The Astronomical Journal 153 (4): 160. doi:10.3847/1538-3881/AA62A9. PMID 29456255. Bibcode: 2017AJ....153..160S.
7. ↑ 7.0 7.1 7.2 Nuñez, N. E.; Nelson, T.; Mukai, K.; Sokoloski, J. L.; Luna, G. J. M. (2016). "Symbiotic Stars in X-Rays. III. Suzaku Observations". The Astrophysical Journal 824 (1): 23. doi:10.3847/0004-637X/824/1/23. Bibcode: 2016ApJ...824...23N.
8. ↑ Skopal, Augustin (2006). "The Light Curves of Classical Symbiotic Stars". Journal of the American Association of Variable Star Observers 35 (1): 163. Bibcode: 2006JAVSO..35..163S. http://articles.adsabs.harvard.edu/pdf/2006JAVSO..35..163S. Retrieved 8 October 2021.
9. ↑ Jarzębowski, T. (1964). "Light Variation of Magnetic Star HD 4174". Acta Astronomica 14: 77. Bibcode: 1964AcA....14...77J. https://articles.adsabs.harvard.edu/pdf/1964AcA....14...77J. Retrieved 30 October 2024.
10. ↑ Skopal, A.; Shugarov, S.; Vaňko, M.; Dubovský, P.; Peneva, S. P.; Semkov, E.; Wolf, M. (2012). "Recent photometry of symbiotic stars". Astronomische Nachrichten 333 (3): 242. doi:10.1002/asna.201111655. Bibcode: 2012AN....333..242S.
11. ↑ 11.0 11.1 Ogle, Patrick; Petersen, Mark; Schaeffer, Tim; McCallum, Lewis; Noriega-Crespo, Alberto; Michael Rich, R.; Sebastian, Biny; Bjork, Carl; Body, Steeve; Chinnasamy, Sendhil; Dreschsler, Marcel; Kottary, Tarun; Sainty, Yann; Sparkman, Patrick; Strottner, Xavier (2025). "SDSO1 is a Ghost Planetary Nebula Bow Shock in Front of M31". arXiv:2507.15834 [astro-ph.GA].
12. ↑ Drechsler, Marcel; Strottner, Xavier; Sainty, Yann; Fesen, Robert A.; Kimeswenger, Stefan; Shull, J. Michael; Falls, Bray; Vergnes, Christophe et al. (2023-01-04). "Discovery of Extensive [O iii] Emission Near M31". Research Notes of the AAS 7 (1): 1. doi:10.3847/2515-5172/acaf7e. ISSN 2515-5172. Bibcode: 2023RNAAS...7....1D.
13. ↑ Fesen, Robert A.; Kimeswenger, Stefan; Shull, J. Michael; Drechsler, Marcel; Strottner, Xavier; Sainty, Yann; Falls, Bray; Vergnes, Christophe et al. (2023-11-01). "The Spatial and Emission Properties of the Large [O iii] Emission Nebula Near M31". The Astrophysical Journal 957 (2): 82. doi:10.3847/1538-4357/acfe0d. ISSN 0004-637X. Bibcode: 2023ApJ...957...82F.
14. ↑ Lumbreras-Calle, A.; Fernández-Ontiveros, J. A.; Infante-Sainz, R.; Akhlaghi, M.; Montoro-Molina, B.; Pérez-Díaz, B.; del Pino, A.; Vives-Arias, H.; Hernán-Caballero, A.; López-Sanjuan, C.; Martín-Guerrero, M. A.; Eskandarlou, S.; Ederoclite, A. (December 2024). "Andromeda's tenuous veil: extensive nebular emission near (yet far from) M31". arXiv:2412.08327 [astro-ph.GA].

* v
* t
* e

Constellation of Andromeda

* Adhil
* Andromeda in Chinese astronomy
* List of Andromeda's satellite galaxies
* List of stars in Andromeda

Stars|

| Bayer|

* α
* β
* γ
* δ
* ε
* ζ
* η
* θ
* ι
* κ
* λ
* μ
* ν
* ξ
* ο
* π
* ρ
* σ
* τ
* υ
* φ
* χ
* ψ
* ω

|

Flamsteed|

* 2
* 3
* 4
* 5
* 6
* 7
* 8
* 9
* 10
* 11
* 12
* 13
* 14
* 15
* 18
* 22
* 23
* 26
* 28
* 32
* 36
* 39
* 41
* 44
* 45
* 47
* 49
* 51
* 55
* 56
* 58
* 59
* 60
* 62
* 63
* 64
* 65
* 66

Variable|

* R
* T
* U
* W
* Z
* RT
* RU
* RV
* RX
* SU
* SW
* TU
* TW
* WZ
* XZ
* AB
* AC
* AD
* AE
* AR
* BM
* BX
* CC
* CN
* DS
* DX
* EG
* ET
* EU
* FF
* GP
* GR
* GY
* HN
* KK
* KX
* KZ
* LL
* LP
* LQ
* OP
* OS
* OU
* PX
* QR
* QV
* QX
* V385
* V455
* V529

HD|

* 3
* 166
* 895
* 1185
* 1606
* 2421
* 2767
* 2942
* 3322
* 3346
* 4778
* 5608
* 5789/5788
* 6114
* 7853
* 8673
* 10307
* 13931
* 14622
* 15082
* 16004
* 16028
* 16175
* 217811
* 220105
* 221246
* 221776
* 222109
* 222399
* 223229
* 224365
* 224801
* 225218

Other|

* 3XMM J004232.1+411314
* 6 Persei
* ADS 48
* Groombridge 34
* HAT-P-6
* HR 178
* HR 8768
* M31-RV
* NGC 44
* NGC 82
* NGC 84
* NGC 91
* NGC 162
* NGC 464
* PA-99-N2
* Ross 248
* WASP-1
* WISE 0146+4234
* WISE J0005+3737
* WISE J004945.61+215120.0

| Exoplanets|

* 14 Andromedae b
* Upsilon Andromedae b
* c
* d
* e
* Gliese 15 Ab
* HD 13931 b
* HD 16175 b
* HAT-P-6b
* HAT-P-32b
* WASP-1b
* WASP-33b

|

| Star clusters|

* Mayall II
* NGC 206
* NGC 272
* NGC 752
* NGC 956
* NGC 7686

|

| Nebulae|

* NGC 7662

|

Galaxies|

| NGC|

* 5
* 11
* 13
* 19
* 21
* 20
* 27
* 39
* 43
* 48
* 49
* 51
* 67
* 68
* 69
* 70
* 71
* 72
* 74
* 76
* 79
* 80
* 81
* 83
* 85
* 86
* 90
* 93
* 94
* 96
* 97
* 108
* 109
* 112
* 140
* 149
* 160
* 169
* 181
* 183
* 184
* 214
* 218
* 226
* 228
* 229
* 233
* 243
* 252
* 258
* 260
* 262
* 280
* 304
* 317
* 389
* 393
* 404
* 425
* 431
* 477
* 478
* 512
* 513
* 523
* 528
* 536
* 668
* 679
* 687
* 700
* 703
* 704
* 705
* 708
* 709
* 710
* 712
* 714
* 717
* 732
* 753
* 759
* 891
* 1000
* 7640
* 7836

|

Numbered|

* I
* II
* III
* IV
* V
* VIII
* IX
* X
* XI
* XVIII
* XIX
* XXI

Other|

* 3C 66A
* 3C 66B
* Andromeda Galaxy
* Donatiello I
* Messier 32
* Messier 110

| Galaxy clusters|

* Abell 262
* NGC 68 group

|

| Astronomical events|

* GRB 101225A
* SN 1885A

|

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