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Not to be confused with χ Herculis.
X Herculis

A visual band light curve for X Herculis, plotted from AAVSO data. The individual measurements were averaged into five day wide bins, to improve signal/noise. [1]
Observation data
Epoch J2000       Equinox J2000
Constellation Hercules
Right ascension 16h 02m 39.17301s [2]
Declination +47° 14′ 25.2653″ [2]
Apparent magnitude (V) 5.8 - 7.0 [3]
Characteristics
Spectral type M8III [4]
Variable type SRb [5]
Astrometry
Radial velocity (Rv)−88.95±0.4 [6] km/s
Proper motion (μ) RA: −68.631±0.260 [2]  mas/ yr
Dec.: 62.824±0.385 [2]  mas/ yr
Parallax (π)8.1621 ± 0.2511  mas [2]
Distance400 ± 10  ly
(123 ± 4  pc)
Details
Mass1.9 [7]  M☉
Radius183±4 [7]  R☉
Luminosity3570 [7]  L☉
Temperature3281±130 [7]  K
Other designations
HD 144205, HIP 78574, SAO 45863, IRC +50248, RAFGL 5317 [8]
Database references
SIMBAD data

X Herculis is a star about 400 light years from the Earth in the constellation Hercules. It is a semiregular variable star, ranging in brightness from magnitude 5.8 to 7.0 over a period of about 102 days. [3] It is rarely visible to the naked-eye, but can be seen easily with a small telescope, or binoculars. [9]

X Herculis was discovered to be a variable star by John Gore, in 1890. Variability was quickly confirmed by two other observers. Although it was known by a variety of names at the time of the discovery of its variability, the star was immediately given the variable star designation X Herculis. [10] Subsequent studies found periods of 102±5, 178.5±5 and 658.3±17 days in the light curve. [7]

X Herculis is an oxygen-rich AGB star, losing mass at a rate of 1.4×10−7  solar masses per year via a stellar wind. [11] In 1986 Benjamin Zuckerman et al. detected the J=2→1 line of carbon monoxide (CO) in the stellar wind. [12] The shape of the CO line profile shows that the wind has two components, one of which leaves the vicinity of the star at a speed of 3.2±0.5 km/sec, and another which has a speed of 9.0±1.0 km/sec. [11] The slow wind appears to arise from a disk surrounding, and possibly orbiting X Herculis. The faster wind appears to arise from a bipolar outflow. [13] The stellar winds have produced a large circumstellar shell. Studies of such a shell using molecular spectroscopy can only probe the inner region of the shell, because as the stellar wind expands and becomes less dense, the molecules in the gas are dissociated by the interstellar radiation field. Luckily, the high galactic latitude (48°) of X Herculis allows the 21 cm line of atomic hydrogen (HI) to be observed without contamination from unrelated material in the galactic plane. Lynn Matthews et al. mapped the HI shell, and found it to be at least 0.8 light years across, with a comet-like tail produced by the motion of the star through the interstellar medium (ISM). The mass of HI in the shell is about 2.1×10−3  solar masses, but the total mass of the shell may be significantly larger, because much of the hydrogen may be in molecular form. [7]

Near-infrared radiation from X Herculis was detected in the first Two-Micron Sky Survey, published in 1969. [14] The stellar winds from AGB stars contain dust and that dust was detected in the far-infrared by the IRAS satellite. The dust emission was resolved by IRAS, showing the same large shell that is seen in HI observations. [15] X Herculis is moving through the ISM at a speed of 108 km/sec. Herschel Space Observatory images show a bow shock in the region where the stellar wind collides with the ISM, but they show no evidence of the bipolar flow seen in high resolution maps of the molecular line emission. [4]

References

  1. ^ "Download Data". aavso.org. AAVSO. Retrieved 25 March 2023.
  2. ^ a b c d e 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. ^ a b "X Her". The International Variable Star Index. AAVSO. Retrieved 26 March 2023.
  4. ^ a b Jorissen, A.; Mayer, A.; Van Eck, S.; Ottensamer, R.; Kerschbaum, F.; Ueta, T.; Bergman, P.; Blommaert, J. A. D. L.; Decin, L.; Groenewegen, M. A. T.; Hron, J.; Nowotny, W.; Olofsson, H.; Posch, Th.; Sjouwerman, L. O.; Vandenbussche, B.; Waelkens, C. (August 2011). "X Herculis and TX Piscium: two cases of ISM interaction with stellar winds observed by Herschel" (PDF). Astronomy and Astrophysics. 532: A135. arXiv: 1106.3645. Bibcode: 2011A&A...532A.135J. doi: 10.1051/0004-6361/201116927. S2CID  59127148. Retrieved 27 March 2023.
  5. ^ Samus', N. N.; Kazarovets, E. V.; Durlevich, O. V.; Kireeva, N. N.; Pastukhova, E. N. (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode: 2017ARep...61...80S. doi: 10.1134/S1063772917010085. S2CID  125853869.
  6. ^ Famaey, B.; Jorissen, A.; Luri, X.; Mayor, M.; Udry, S.; Dejonghe, H.; Turon, C. (January 2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters" (PDF). Astronomy and Astrophysics. 430: 165–186. arXiv: astro-ph/0409579. Bibcode: 2005A&A...430..165F. doi: 10.1051/0004-6361:20041272. S2CID  17804304. Retrieved 27 March 2023.
  7. ^ a b c d e f Matthews, L. D.; Libert, Y.; Gérard, E.; Le Bertre, T.; Johnson, M. C.; Dame, T. M. (February 2011). "H I Observations of the Asymptotic Giant Branch Star X Herculis: Discovery of an Extended Circumstellar Wake Superposed on a Compact High-velocity Cloud". The Astronomical Journal. 141 (2): 60. arXiv: 1011.6383. Bibcode: 2011AJ....141...60M. doi: 10.1088/0004-6256/141/2/60. S2CID  16083069. Retrieved 27 March 2023.
  8. ^ "V* X Her -- Asymptotic Giant Branch Star". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2023-03-25.
  9. ^ Taylor, Melvyn. "Observing Variable Stars with Binoculars" (PDF). British Astronomical Association. Retrieved 24 March 2023.
  10. ^ Gore, J. E. (July 16, 1890). "A New Variable Star in Hercules". Astronomische Nachrichten. 125 (5): 79. Bibcode: 1890AN....125...79G. doi: 10.1002/asna.18901250511. Retrieved 26 March 2023.
  11. ^ a b Knapp, G. R.; Young, K.; Lee, E.; Jorissen, A. (July 1998). "Multiple Molecular Winds in Evolved Stars. I. A Survey of CO(2-1) and CO(3-2) Emission from 45 Nearby Asymptotic Giant Branch Stars". The Astrophysical Journal Supplement Series. 117 (1): 209–231. arXiv: astro-ph/9711125. Bibcode: 1998ApJS..117..209K. doi: 10.1086/313111. S2CID  15210237. Retrieved 27 March 2023.
  12. ^ Zuckerman, B.; Dyke, H. M. (May 1986). "Carbon Monoxide Emission from Stars in the IRAS and Revised AFGL Catalogs. I. Mass Loss Driven by Radiation Pressure on Dust Grains". Astrophysical Journal. 304: 394. Bibcode: 1986ApJ...304..394Z. doi: 10.1086/164173. Retrieved 27 March 2023.
  13. ^ Nakashima, Jun-ichi (February 2005). "Disklike Structure in the Semiregular Pulsating Star X Herculis". The Astrophysical Journal. 620 (2): 943–947. arXiv: astro-ph/0411021. Bibcode: 2005ApJ...620..943N. doi: 10.1086/427145. S2CID  10132237. Retrieved 27 March 2023.
  14. ^ Neugebauer, G.; Leighton, R. B. (1969). Two-micron sky survey. A preliminary catalogue. NASA. Bibcode: 1969tmss.book.....N. Retrieved 24 March 2023.
  15. ^ Young, K.; Phillips, T. G.; Knapp, G. R. (June 1993). "Circumstellar Shells Resolved in the IRAS Survey Data. I. Data Processing Procedure, Results, and Confidence Tests". Astrophysical Journal Supplement. 86: 517–640. Bibcode: 1993ApJS...86..517Y. doi: 10.1086/191789.
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