Discovery of a faint companion to alcor using MMT/AO 5 μm imaging

Eric E. Mamajek, Matthew A. Kenworthy, Philip M Hinz, Michael R. Meyer

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

We report the detection of a faint stellar companion to the famous nearby A5V star Alcor (80UMa). The companion has M-band (λ = 4.8μm) magnitude 8.8 and projected separation 111 (28 AU) from Alcor. The companion is most likely a low-mass (∼0.3M ) active star which is responsible for Alcor's X-ray emission detected by ROSAT (L X ≃ 10 28.3ergs-1). Alcor is a nuclear member of the Ursa Major star cluster (UMa; d ≃ 25pc, age ≃ 0.5Gyr), and has been occasionally mentioned as a possible distant (709″) companion of the stellar quadruple Mizar (ζUMa). Comparing the revised Hipparcos proper motion for Alcor with the mean motion for otherUMa nuclear members shows that Alcor has a peculiar velocity of 1.1kms-1, which is comparable to the predicted velocity amplitude induced by the newly discovered companion (∼1kms-1). Using a precise dynamical parallax for Mizar and the revised Hipparcos parallax for Alcor, we find that Mizar and Alcor are physically separated by 0.36 ± 0.19pc (74 39kAU; minimum 18kAU), and their velocity vectors are marginally consistent (χ2 probability 6%). Given their close proximity and concordant motions we suggest that the Mizar quadruple and the Alcor binary be together considered the second closest stellar sextuplet. The addition of Mizar-Alcor to the census of stellar multiples with six or more components effectively doubles the local density of such systems within the local volume (d < 40pc).

Original languageEnglish (US)
Pages (from-to)919-925
Number of pages7
JournalAstronomical Journal
Volume139
Issue number3
DOIs
StatePublished - 2010

Fingerprint

parallax
stars
census
star clusters
proper motion
proximity
x rays
detection

Keywords

  • Binaries: close
  • Binaries: general
  • Binaries: visual
  • Open clusters and associations: individual (Ursa Major)
  • Stars: individual (Alcor, Mizar)

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Discovery of a faint companion to alcor using MMT/AO 5 μm imaging. / Mamajek, Eric E.; Kenworthy, Matthew A.; Hinz, Philip M; Meyer, Michael R.

In: Astronomical Journal, Vol. 139, No. 3, 2010, p. 919-925.

Research output: Contribution to journalArticle

Mamajek, Eric E. ; Kenworthy, Matthew A. ; Hinz, Philip M ; Meyer, Michael R. / Discovery of a faint companion to alcor using MMT/AO 5 μm imaging. In: Astronomical Journal. 2010 ; Vol. 139, No. 3. pp. 919-925.
@article{bee7efc529004d54b42f18d34b2948d0,
title = "Discovery of a faint companion to alcor using MMT/AO 5 μm imaging",
abstract = "We report the detection of a faint stellar companion to the famous nearby A5V star Alcor (80UMa). The companion has M-band (λ = 4.8μm) magnitude 8.8 and projected separation 111 (28 AU) from Alcor. The companion is most likely a low-mass (∼0.3M ⊙) active star which is responsible for Alcor's X-ray emission detected by ROSAT (L X ≃ 10 28.3ergs-1). Alcor is a nuclear member of the Ursa Major star cluster (UMa; d ≃ 25pc, age ≃ 0.5Gyr), and has been occasionally mentioned as a possible distant (709″) companion of the stellar quadruple Mizar (ζUMa). Comparing the revised Hipparcos proper motion for Alcor with the mean motion for otherUMa nuclear members shows that Alcor has a peculiar velocity of 1.1kms-1, which is comparable to the predicted velocity amplitude induced by the newly discovered companion (∼1kms-1). Using a precise dynamical parallax for Mizar and the revised Hipparcos parallax for Alcor, we find that Mizar and Alcor are physically separated by 0.36 ± 0.19pc (74 39kAU; minimum 18kAU), and their velocity vectors are marginally consistent (χ2 probability 6{\%}). Given their close proximity and concordant motions we suggest that the Mizar quadruple and the Alcor binary be together considered the second closest stellar sextuplet. The addition of Mizar-Alcor to the census of stellar multiples with six or more components effectively doubles the local density of such systems within the local volume (d < 40pc).",
keywords = "Binaries: close, Binaries: general, Binaries: visual, Open clusters and associations: individual (Ursa Major), Stars: individual (Alcor, Mizar)",
author = "Mamajek, {Eric E.} and Kenworthy, {Matthew A.} and Hinz, {Philip M} and Meyer, {Michael R.}",
year = "2010",
doi = "10.1088/0004-6256/139/3/919",
language = "English (US)",
volume = "139",
pages = "919--925",
journal = "Astronomical Journal",
issn = "0004-6256",
publisher = "IOP Publishing Ltd.",
number = "3",

}

TY - JOUR

T1 - Discovery of a faint companion to alcor using MMT/AO 5 μm imaging

AU - Mamajek, Eric E.

AU - Kenworthy, Matthew A.

AU - Hinz, Philip M

AU - Meyer, Michael R.

PY - 2010

Y1 - 2010

N2 - We report the detection of a faint stellar companion to the famous nearby A5V star Alcor (80UMa). The companion has M-band (λ = 4.8μm) magnitude 8.8 and projected separation 111 (28 AU) from Alcor. The companion is most likely a low-mass (∼0.3M ⊙) active star which is responsible for Alcor's X-ray emission detected by ROSAT (L X ≃ 10 28.3ergs-1). Alcor is a nuclear member of the Ursa Major star cluster (UMa; d ≃ 25pc, age ≃ 0.5Gyr), and has been occasionally mentioned as a possible distant (709″) companion of the stellar quadruple Mizar (ζUMa). Comparing the revised Hipparcos proper motion for Alcor with the mean motion for otherUMa nuclear members shows that Alcor has a peculiar velocity of 1.1kms-1, which is comparable to the predicted velocity amplitude induced by the newly discovered companion (∼1kms-1). Using a precise dynamical parallax for Mizar and the revised Hipparcos parallax for Alcor, we find that Mizar and Alcor are physically separated by 0.36 ± 0.19pc (74 39kAU; minimum 18kAU), and their velocity vectors are marginally consistent (χ2 probability 6%). Given their close proximity and concordant motions we suggest that the Mizar quadruple and the Alcor binary be together considered the second closest stellar sextuplet. The addition of Mizar-Alcor to the census of stellar multiples with six or more components effectively doubles the local density of such systems within the local volume (d < 40pc).

AB - We report the detection of a faint stellar companion to the famous nearby A5V star Alcor (80UMa). The companion has M-band (λ = 4.8μm) magnitude 8.8 and projected separation 111 (28 AU) from Alcor. The companion is most likely a low-mass (∼0.3M ⊙) active star which is responsible for Alcor's X-ray emission detected by ROSAT (L X ≃ 10 28.3ergs-1). Alcor is a nuclear member of the Ursa Major star cluster (UMa; d ≃ 25pc, age ≃ 0.5Gyr), and has been occasionally mentioned as a possible distant (709″) companion of the stellar quadruple Mizar (ζUMa). Comparing the revised Hipparcos proper motion for Alcor with the mean motion for otherUMa nuclear members shows that Alcor has a peculiar velocity of 1.1kms-1, which is comparable to the predicted velocity amplitude induced by the newly discovered companion (∼1kms-1). Using a precise dynamical parallax for Mizar and the revised Hipparcos parallax for Alcor, we find that Mizar and Alcor are physically separated by 0.36 ± 0.19pc (74 39kAU; minimum 18kAU), and their velocity vectors are marginally consistent (χ2 probability 6%). Given their close proximity and concordant motions we suggest that the Mizar quadruple and the Alcor binary be together considered the second closest stellar sextuplet. The addition of Mizar-Alcor to the census of stellar multiples with six or more components effectively doubles the local density of such systems within the local volume (d < 40pc).

KW - Binaries: close

KW - Binaries: general

KW - Binaries: visual

KW - Open clusters and associations: individual (Ursa Major)

KW - Stars: individual (Alcor, Mizar)

UR - http://www.scopus.com/inward/record.url?scp=76949098184&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=76949098184&partnerID=8YFLogxK

U2 - 10.1088/0004-6256/139/3/919

DO - 10.1088/0004-6256/139/3/919

M3 - Article

VL - 139

SP - 919

EP - 925

JO - Astronomical Journal

JF - Astronomical Journal

SN - 0004-6256

IS - 3

ER -