HR 4796

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HR 4796
Dust ring around HR 4796A (eso1417a).jpg
A dust ring encircles HR 4796's primary star
Observation data
Epoch J2000.0       Equinox J2000.0
Constellation Centaurus [1]
A
Right ascension 12h 36m 01.0318s [2]
Declination −39° 52′ 10.223″ [2]
Apparent magnitude  (V)5.77 [3]
B
Right ascension 12h 36m 00.5491s [4]
Declination −39° 52′ 15.694″ [4]
Apparent magnitude  (V)13.30 [3]
Characteristics
A
Evolutionary stage main sequence [5] [2]
Spectral type A0 V [6]
B−V color index +0.01 [7]
B
Evolutionary stage pre-main-sequence [8]
Spectral type M2.5 V [6]
Astrometry
A
Radial velocity (Rv)+10.95±0.59 [2] km/s
Proper motion (μ)RA: −55.653 [2] mas/yr
Dec.: −23.880 [2] mas/yr
Parallax (π)14.1300±0.0471  mas [2]
Distance 230.8 ± 0.8  ly
(70.8 ± 0.2  pc)
Absolute magnitude  (MV)+1.46 [3]
B
Radial velocity (Rv)+6.27±6.72 [4] km/s
Proper motion (μ)RA: −59.064 [4] mas/yr
Dec.: −30.026 [4] mas/yr
Parallax (π)14.1490±0.0220  mas [4]
Distance 230.5 ± 0.4  ly
(70.7 ± 0.1  pc)
Absolute magnitude  (MV)+8.99 [3]
Details
Component A
Mass 2.18±0.10 [9]   M☉
Radius 1.68 [9]   R☉
Luminosity 23 [9]   L☉
Surface gravity (log g)4.43 [10]   cgs
Temperature 9,378 [10]   K
Metallicity [Fe/H]–0.03 [10]   dex
Rotational velocity (v sin i)152 [11]  km/s
Age 8±2 [6]   Myr
Component B
Mass 0.3 [12]   M☉
Radius 0.89 [13]   R☉
Luminosity0.130 [13]   L☉
Surface gravity (log g)4.26 [13]   cgs
Temperature 3,664 [13]   K
Rotational velocity (v sin i)12.1 [14]  km/s
Age 8±2 [6]   Myr
Other designations
CD−39°7717, CPD−39°5622, GC 17164, HD 109573, HIP 61498, HR 4796, SAO 203621, CCDM J12360-3952, 2MASS J12360103-3952102 [15]
Database references
SIMBAD data

HR 4796 is a binary star system in the southern constellation of Centaurus. Parallax measurements put it at a distance of 235 light-years (72 parsecs ) from the Earth. The two components of this system have an angular separation of 7.7 arcseconds, which, at their estimated distance, is equivalent to a projected separation of about 560 Astronomical Units (AU), or 560 times the separation of the Earth from the Sun. [6] The star and its ring resemble an eye, and it is sometimes known by the nickname "Sauron's Eye". [16] [17]

Contents

Components

This is a young system with an estimated age of about 8 million years. [6] The primary member A has a stellar classification of A0 V, while its smaller companion B is a red dwarf with a classification of M2.5 V. [6] The luminosity class of 'V' indicates that both stars belong to the main sequence and are generating energy through the thermonuclear fusion of hydrogen at their cores. The primary is emitting this energy from its outer envelope at an effective temperature of about 9,378 K, which gives it the white hue characteristic of A-type stars. [10] [18] It has a radius about 168% of the radius of the Sun and 218% of the Sun's mass. [9] The abundance of elements other than hydrogen or helium, what astronomers term the star's metallicity, is similar to the proportion in the Sun. [6]

The secondary has only 30% of a solar mass and is still contracting towards the main sequence. It is still around the size of the Sun, although much less luminous because of its low temperature. Its brightness varies in an irregular manner and it is considered to be a T Tauri star. An X-ray flare has also been observed. [19]

Debris disk

Hubble image of dust structure surrounding HR 4796A Circumstellar Disk Around HR 4796A (Hubble) (2019-29-4504-Image).png
Hubble image of dust structure surrounding HR 4796A

In 1991, the primary was found to have an excess of infrared emission, implying that it has a circumstellar debris disk. Observations using the Near-Infrared Multi-Object Spectrometer aboard the Hubble Space Telescope in 2007 indicated that the dust had a reddish spectrum similar to that of tholins. [20] The disk was resolved with the Hubble Space Telescope in 2009, confirming that it exists. Based on these images, the disk has a radius of 75 AU and a width of less than 18.5 AU. It may have some asymmetries and the center appears to be slightly offset from the star. The dust in the disk is likely the result of collisions between larger particles. [6] In 2011, observations of the ring offset by the Subaru Telescope implies that one or more planets would likely exist within gaps tugging at its dust grains. [21] [22] With a new image in 2014, the configuration and alignment of the dust ring and HR4796A has been nicknamed "Eye of Sauron". [16] [17]

In 2017 a group using NASA/IRTF and Spitzer infrared spectroscopy of the infrared excess determined that the bright narrow ring is made up of very red devolatilzed cometary material, and that a second faint, hot diffuse dust component likely due to inspiralling material escaping from the ring was present close to the star and evaporating. [23] The discovery of a complex dust structure about 1,600 AU across, enveloping HR 4796A, was announced in March 2018. The structure is believed to have been formed by the pressure of starlight from HR 4796A expelling dust from the debris disk far into space. The structure is much more extended in one direction than the other, possibly due to either the motion of HR 4796A through the interstellar medium, or the gravitational influence of HR 4796B. [24]

Kinematics

The space velocity of HR 4796 in the Galactic coordinate system is [U, V, W] = [−8.5, −18.3, −3.6] km s−1. This trajectory and the location of the system suggests that it may be a member of the TW Hydrae association of stars that share a common origin. [25] A low-mass member of this association, identified as 2MASS J12354893−3950245, may be a tertiary component of the HR 4796 system. It has a proper motion matching HR 4796, suggesting it is gravitationally bound to the other two stars, and is separated from the pair by a distance of about 13,500 AU. [26]

References

  1. ↑ Roman, Nancy G. (1987). "Identification of a constellation from a position". Publications of the Astronomical Society of the Pacific . 99 (617): 695. Bibcode:1987PASP...99..695R. doi: 10.1086/132034 . Constellation record for this object at VizieR.
  2. 1 2 3 4 5 6 7 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.
  3. 1 2 3 4 Bell, Cameron P. M.; Mamajek, Eric E.; Naylor, Tim (2015). "A self-consistent, absolute isochronal age scale for young moving groups in the solar neighbourhood". Monthly Notices of the Royal Astronomical Society. 454 (1): 593. arXiv: 1508.05955 . Bibcode:2015MNRAS.454..593B. doi: 10.1093/mnras/stv1981 .
  4. 1 2 3 4 5 6 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.
  5. ↑ Zorec, J.; Royer, F. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities". Astronomy and Astrophysics. 537: A120. arXiv: 1201.2052 . Bibcode:2012A&A...537A.120Z. doi:10.1051/0004-6361/201117691.
  6. 1 2 3 4 5 6 7 8 9 Schneider, G.; et al. (January 2009), "STIS Imaging of the HR 4796A Circumstellar Debris Ring", The Astronomical Journal, 137 (1): 53–61, arXiv: 0810.0286 , Bibcode:2009AJ....137...53S, doi:10.1088/0004-6256/137/1/53, S2CID   35159109
  7. ↑ Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J
  8. ↑ Scholz, Alexander; Coffey, Jaime; Brandeker, Alexis; Jayawardhana, Ray (2007). "Rotation and Activity of Pre-Main-Sequence Stars". The Astrophysical Journal. 662 (2): 1254. arXiv: 0704.3266 . Bibcode:2007ApJ...662.1254S. doi:10.1086/518361.
  9. 1 2 3 4 Gerbaldi, M.; et al. (June 1999), "Search for reference A0 dwarf stars: Masses and luminosities revisited with HIPPARCOS parallaxes", Astronomy and Astrophysics Supplement, 137 (2): 273–292, Bibcode:1999A&AS..137..273G, doi: 10.1051/aas:1999248
  10. 1 2 3 4 Saffe, C.; et al. (October 2008), "Spectroscopic metallicities of Vega-like stars", Astronomy and Astrophysics, 490 (1): 297–305, arXiv: 0805.3936 , Bibcode:2008A&A...490..297S, doi:10.1051/0004-6361:200810260, S2CID   15059920
  11. ↑ Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics, 463 (2): 671–682, arXiv: astro-ph/0610785 , Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224, S2CID   18475298
  12. ↑ Huélamo, N.; et al. (December 2004), "Rotation periods of Post-T Tauri stars in Lindroos systems", Astronomy and Astrophysics, 428 (3): 953–967, arXiv: astro-ph/0408226 , Bibcode:2004A&A...428..953H, doi:10.1051/0004-6361:20034442, S2CID   10656237
  13. 1 2 3 4 Stassun, Keivan G.; et al. (2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv: 1905.10694 . Bibcode:2019AJ....158..138S. doi: 10.3847/1538-3881/ab3467 .
  14. ↑ Jayawardhana, Ray; Coffey, Jaime; Scholz, Alexander; Brandeker, Alexis; Van Kerkwijk, Marten H. (2006). "Accretion Disks around Young Stars: Lifetimes, Disk Locking, and Variability". The Astrophysical Journal. 648 (2): 1206. arXiv: astro-ph/0605601 . Bibcode:2006ApJ...648.1206J. doi:10.1086/506171.
  15. ↑ "HD 109573 -- Star in double system", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2007-01-08
  16. 1 2 Flora Graham (4 June 2014). "Eye of Sauron star spotted by planet-hunting camera". New Scientist.
  17. 1 2 NewsCorp Australia (6 June 2014). "Sauron's Eye has been found. And it's watching us all, from above, in the form of ringed star HR 4796A". Courier Mail.
  18. ↑ "The Colour of Stars", Australia Telescope, Outreach and Education, Commonwealth Scientific and Industrial Research Organisation, December 21, 2004, archived from the original on March 18, 2012, retrieved 2012-01-16
  19. ↑ López-Santiago, J.; Crespo-Chacón, I.; Micela, G.; Reale, F. (2010). "A Detailed Study of the Rise Phase of a Long Duration X-Ray Flare in the Young Star TWA 11B". The Astrophysical Journal. 712 (1): 78. arXiv: 1002.1013 . Bibcode:2010ApJ...712...78L. doi:10.1088/0004-637X/712/1/78.
  20. ↑ Debes, J. H.; Weinberger, A. J.; Schneider, G. (2008). "Complex Organic Materials in the Circumstellar Disk of HR 4796A". Astrophysical Journal Letters. 673 (2): L191. arXiv: 0712.3283 . Bibcode:2008ApJ...673L.191D. doi:10.1086/527546. S2CID   1215872.
  21. ↑ "Subaru's sharp eye confirms signs of unseen planets in star's dust ring". Astronomy Magazine. 2012-01-04.
  22. ↑ Thalmann, C.; et al. (December 2011), "Images of the Extended Outer Regions of the Debris Ring around HR 4796 A", The Astrophysical Journal Letters, 743 (1): L6 (2011), arXiv: 1110.2488 , Bibcode:2011ApJ...743L...6T, doi:10.1088/2041-8205/743/1/L6, S2CID   14131310
  23. ↑ Lisse, C.; Sitko, M.; Marengo, M.; et al. (November 2017). "Infrared Spectroscopy of HR 4796Aʼs Bright Outer Cometary Ring+Tenuous Inner Hot Dust Cloud". The Astronomical Journal. 154 (5): 182. arXiv: 1708.02834 . Bibcode:2017AJ....154..182L. doi: 10.3847/1538-3881/aa855e . S2CID   119466875.
  24. ↑ Hille, Karl (6 March 2018). "Hubble Finds Huge System of Dusty Material Enveloping the Young Star HR 4796A". NASA. Retrieved 8 March 2018.
  25. ↑ Makarov, Valeri V. (March 2007), "Unraveling the Origins of Nearby Young Stars" (PDF), The Astrophysical Journal Supplement Series, 169 (1): 105–119, Bibcode:2007ApJS..169..105M, doi:10.1086/509887, S2CID   119552302
  26. ↑ Kastner, J. H.; Zuckerman, B.; Bessell, M. (December 2008), "Identification of the TW Hydrae association member 2M1235-39: a tertiary component of the HR 4796 system", Astronomy and Astrophysics, 491 (3): 829–831, arXiv: 0808.2630 , Bibcode:2008A&A...491..829K, doi:10.1051/0004-6361:200810580, S2CID   118436645
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