雙星榜

mca

雙星最宜目視觀賞，用相機拍攝反而失去樂趣 !

以下是一些典型的目視雙星，大部份都可以用小鏡分辨，表中的 Pri (Primary) 是主星，通常指較亮的一顆；Sec (Secondary) 是伴星；Separation 是兩星的角距；PA (Position angle) 是伴星的方位角，從主星的北位反時針方向量度；Color 是星的大約顏色，星越暗，人眼的顏色感越遲鈍，所以顏色只供參考，不能作實。


        


        


        


        


        


在天鵝座的 Beta Cyg (Albireo) 和 大犬座的 h3945 (h 指 Herschel 編號) 是公認最美的孖寶，前者在北半球的夏天見到，後者在冬天見到，外觀與 Albireo 相似，故此又叫 "Winter Albireo"，不看走寶。Rigel 的主星較伴星亮五百倍，Castor 雙星只距四角秒，它們宜用 100X 以上觀測。The Trapezium (獵戶座) 與 The Double Double (天琴座) 也是必看的聚星系統，用大小鏡看均宜。


在攝影術還未普及的年代，雙星是重要的天體測量項目。通過長期觀測物理雙星的角距和方位角，天文學家可以研究雙星系統的互繞軌道，再測定它們的距離便可算出主伴兩星的質量。
(參考：怎樣測定恆星的質量和直徑 http://forum.hkas.org.hk/viewthread.php?tid=3801&extra=page%3D6)

WFC-3

謝謝Alan 的分享,這是非常有用的資料!

jojomamani

Alan alway share his amazing experience! Thx!

BillYeung

Thanks Alan,

For some reason I have been very interested in wide separation double stars. The fact that a pair of double could be >0.16 LY apart really amazed me.

Epsilon Lyrae
From Wikipedia, the free encyclopediaJump to: navigation, search
"The Double Double" redirects here. For other uses, see double-double (disambiguation).
Epsilon Lyrae Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Lyra
Epsilon1 Lyrae
Right ascension 18h 44m 20.3453s
Declination +39° 40′ 12.444″
Apparent magnitude (V) 4.7
Epsilon2 Lyrae
Right ascension 18h 44m 22.7803s
Declination +39° 36′ 45.798″
Apparent magnitude (V) 5.1
Characteristics
Spectral type F1V / A8V
Astrometry

Parallax (π) 20.10 ± 0.76 mas
Distance 162 ± 6 ly
(50 ± 2 pc)

Other designations
4 Lyr, HR 7051, HD 173582, HIP 91919, BD +39 03509, SAO 67310, ADS 11635, CCDM 18443+3938, TYC 03122-3438 2, GSC 03122-3438
Database references
SIMBAD data
Database references
SIMBAD data

Epsilon Lyrae (ε Lyr / ε Lyrae), commonly quoted as The Double Double, is a quadruple system approximately 162 light-years away in the constellation of Lyra. It can easily be separated into two components when viewed through binoculars, or even with the naked eye under excellent conditions. The northern star is called ε1 and the southern one is called ε2; they both lie around 162 light years from Earth and orbit each other. When viewed at higher magnifications, both stars of the binary can be further split into binaries; that is, the system contains two binary stars orbiting each other. Being able to view the components of each is a common benchmark for the resolving power of telescopes, since the individual doubles are so close together: the stars of ε1 were 2.35 arc-seconds apart in 2006, those of ε2 were separated by about the same amount in that year. Since the first high-precision measurements of their orbit in the 1980s, both binaries have moved only a few degrees in position angle.

The component stars of ε1 have magnitudes of 4.7 and 6.2 separated by 2.6" and have an orbital period that can only be crudely estimated at 1200 years, which places them at roughly 140 AU apart. The component stars of ε2 have magnitudes 5.1 and 5.5 separated by 2.3", and orbit in perhaps half that period. ε1 and ε2 themselves are no closer than 0.16 light years apart, and would take hundreds of thousands of years to complete an orbit. An observer at either pair would see the other pair shining with the light of a quarter Moon, l ess than a degree away from each other.[1] [2]

A fifth component of this system, orbiting one of the ε2 pair, was detected by speckle interferometry in 1985 and confirmed in two subsequent observations. No orbit can be prepared from such limited data, but its rapid motion suggests a period of a few tens of years. Its maximum observed separation of 0.2 arc-seconds precludes direct visual observation.

BillYeung

Mizar (star)
From Wikipedia, the free encyclopediaJump to: navigation, search
This is an article about the star, for other uses please see Mizar (disambiguation)
Mizar
Mizar and Alcor in constellation Ursa Major.
Observation data
Epoch J2000      Equinox J2000
Constellation Ursa Major
Right ascension 13h 23m 55.5s
Declination +54° 55′ 31″
Apparent magnitude (V) 2.23
Characteristics
Spectral type A2 V/A2 V/A1 V
U−B color index 0.09
B−V color index 0.13
Astrometry

Radial velocity (Rv) −9 km/s
Proper motion (μ) RA: 121.23 mas/yr
Dec.: −22.01 mas/yr
Parallax (π) 41.73 ± 0.61 mas
Distance 78 ± 1 ly
(24 ± 0.4 pc)
Absolute magnitude (MV) 0.33

Other designations
Mizat, Mirza, Mitsar, Vasistha, 79 Ursae Majoris, HR 5054, BD +55 1598A, HD 116656, SAO 28737, FK5 497, HIP 65378.




Alcor Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Ursa Major
Right ascension 13h 25m 13.5s
Declination +54° 59' 17"
Apparent magnitude (V) +3.99
Absolute magnitude (V) +2.01
Distance 81.2 ± 1.2 ly
(24.9 ± 0.4 pc)
Spectral type A5V
Other designations
Saidak, Suha, Arundhati, g Ursae Majoris, 80 Ursae Majoris, HR 5062, HD 116842, BD +55 1603, HIP 65477, SAO 28751

The Mizar-Alcor stellar sextuple system consists of the quadruplet system Mizar and the binary system Alcor.

Mizar (ζ UMa / ζ Ursae Majoris) is a quadruplet system of two binary stars in the constellation Ursa Major and is the second star from the end of the Big Dipper's handle. Its apparent magnitude is 2.23 and its spectral class is A1V. Mizar's name comes from the Arabic مئزر mīzar, meaning a waistband or girdle.)

With normal eyesight one can make out a faint companion just to the east, named Alcor or 80 Ursae Majoris. Alcor is of magnitude 3.99 and spectral class A5V. Mizar and Alcor together are sometimes called the "Horse and Rider," and the ability to resolve the two stars with the naked eye is often quoted as a test of eyesight, although even people with quite poor eyesight can see the two stars. Arabic literature says that only those with the sharpest eyesight can see the companion of Mizar. Astronomer Sir Patrick Moore has suggested that this in fact refers to another star which lies visually between Mizar and Alcor. Mizar and Alcor lie three light-years apart, and though their proper motions show they move together (they are both members of the Ursa Major Moving Group), it was long believed they do not form a true binary star system, but simply a double star. However, in 2009, it was reported by astronomer Eric Mamajek and collaborators that Alcor actually is itself a binary, consisting of Alcor A and Alcor B, and that this binary system is most likely gravitationally bound to Mizar, bringing the full count of stars in this complex system to six.[1] Their study also demonstrated that the Alcor binary and Mizar quadruple are much closer together than previously thought - approximately 74,000 ± 39,000 Astronomical Units.[2]
The whole four-star system lies about 78 light-years away from Earth. The components are all members of the Ursa Major moving group, a mostly dispersed group of stars sharing a common birth, as determined by proper motion. The other stars of the Big Dipper, except Dubhe and Alkaid, belong to this group as well.

mca

(回應 #4)

物理上 The Double Double 的確是一個聚星系統，它離地球 160 光年，所以較易觀測它們的軌道。ε1 雙星互繞周期 1200 年，ε2 雙星互繞周期 580 年，兩對雙星 (ε1、ε2) 互繞周期未知，可能是幾十萬年。

在學會成立之前，同好的私伙鏡大部份都是 60 mm 或 75 mm 的長焦折射 (f/12 或 f/15)，用 ε1 和 ε2 來鬥小鏡的分辨能力 (resolving power) 是初哥觀星節目之一。以 Dawes limit 計，6 cm 折射的理論分辨能力只有 1.9 角秒，好 seeing 時可見 ε2 (或 ε1) 勉強分開，用 75 mm 鏡看就差不多分開了。無鏡的人就肉眼鬥肉眼看 ε1 是否與 ε2 分開 (兩者角距 3.5 角分)，不過見不見到 "分開" 只有自己心知，有 D 吾衰得會死撑