类太阳恒星
类太阳恒星包括太阳型恒星(solar-type star)、太阳相似体(solar analog)、孪生太阳(solar twin)等,是与太阳特别相似的那些恒星。这样的分类是有阶层性的,孪生是与太阳最接近的,其次是相似体,最后是太阳型[1]。观察这些恒星最重要的是能更好的理解太阳与其他恒星相关的各种性质,特别是恒星与行星的适居性。
与太阳相似的
[编辑]这三种与太阳相似度类型的定义,反映出天文观测技术的演变。起初,太阳型恒星的定义只是考虑与太阳最接近的相似性。然后,观测技术的改善可以提供更精确的关键测量,像是温度,可以筛检出与太阳更为相似的恒星。最后,在技术上的改善使精确度持续的提升,孪生太阳是与太阳几乎完全相同的恒星。
太阳的相似度可以检查一些得到的数值 -像是温度,可以从色指数推导,较之下,只有太阳的温度是可以经由直接的测量获得,是唯一确认无误的[1]。对于和太阳不同的恒星,就不会进行交叉的比对[2]。
太阳型恒星
[编辑]这些恒星大致上与太阳相似,它们都是主序星,B-V色指数在0.48至0.80之间,而太阳的B-V色指数为0.65。或者,可以使用基于光谱类型的定义,如从F8 V至K2 V,这将对应于0.50至1.00的B-V色指数[1]。这样的类太阳恒星清单将会相当广泛,大约有10%的恒星会适合这样的定义[来源请求]。
太阳型恒星显示它们的自转速率和色球活动(如钙的H和K线的发射)与日冕活动(例如X射线辐射)之间有高度的相关性[来源请求]。当太阳型恒星因为主序星生命期中的磁制动而降低自转速率,这些也与年龄有粗略的相关性。Mamajek和Hillenbrand (2008)[3]曾经以它们的色球活动为基础(通过衡量钙的H和K发射谱线)估计距离在16秒差距内的108颗太阳型(F8V — K2V)主序恒星的年龄。
下表列出基于目前的测量,在50光年的距离内,类太阳恒星中满足太阳型恒星的样品。
恒星名称 | J2000座标[4] | 距离[4] (ly) |
恒星 分类[4] |
温度 (K) |
金属量 (dex) |
注解 | |
---|---|---|---|---|---|---|---|
赤经 | 赤纬 | ||||||
波江座ε | 03h 32m 55.8s | -09° 27′ 29.7″ | 10.5 | K2V | 5,153 | –0.11 | [5] |
鲸鱼座τ | 01h 44m 04.1s | -15° 56′ 15″ | 11.9 | G8V | 5,344 | –0.52 | [6] |
波江座40A | 04h 15m 16.3s | -07° 39′ 10″ | 16.5 | K1V | 5,126 | –0.31 | [6] |
波江座82 | 03h 19m 55.7s | -43° 04′ 11.2″ | 19.8 | G8V | 5,338 | –0.54 | [7] |
孔雀座δ | 20h 08m 43.6s | -66° 10′ 55″ | 19.9 | G8IV | 5,604 | +0.33 | [5] |
HR 7722 | 20h 15m 17.4s | -27° 01′ 59″ | 28.8 | K2V | 5,166 | –0.04 | [5] |
格利泽86A | 02h 10m 25.9s | -50° 49′ 25″ | 35.2 | G9V | 5,163 | -0.24 | [6] |
双鱼座54 | 00h 39m 21.8s | +21° 15′ 02″ | 36.1 | K0V | 5,129 | +0.19 | [7] |
御夫座V538 | 05h 41m 20.3s | +53° 28′ 51.8″ | 39.9 | K1V | 3,500-5,000 | -0.20 | [7] |
HD 14412 | 02h 18m 58.5s | -25° 56′ 45″ | 41.3 | G5V | 5,432 | -0.46 | [7] |
HR 4587 | 12h 00m 44.3s | -10° 26′ 45.7″ | 42.1 | G8IV | 5,538 | 0.18 | [7] |
HD 172051 | 18h 38m 53.4s | -21° 03′ 07″ | 42.7 | G5V | 5,610 | -0.32 | [7] |
武仙座72 | 17h 20m 39.6s | +32° 28′ 04″ | 46.9 | G0V | 5,662 | -0.37 | [7] |
HD 196761 | 20h 40m 11.8s | -23° 46′ 26″ | 46.9 | G8V | 5,415 | -0.31 | [5] |
豺狼座Nu² | 15h 21m 48.1s | -48° 19′ 03″ | 47.5 | G4V | 5,664 | -0.34 | [5] |
太阳相似体
[编辑]这些恒星是在光度计的测量下与太阳相似,有以下的性质:
- 与太阳的温度差异在500 K以内(大约在5,200至6,300K)
- 金属量是太阳的50—200%(± 0.3 dex),意味着这些恒星的原行星盘有类似于太阳的尘埃数量,可以让行星形成。
- 没有靠近的伴星(轨道周期为十天或更短),因为这样的伴星会激化恒星的活动。
类太阳恒星不能满足更严谨的孪生太阳标准,在50光年距离之内的类太阳恒星以距离的递增列于下表:
恒星名称 | J2000座标[4] | 距离[4] (ly) |
恒星 分类[4] |
温度 (K) |
金属量 (dex) |
注解 | |
---|---|---|---|---|---|---|---|
赤经 | 赤纬 | ||||||
半人马座α A | 14h 39m 36.5s | -60° 50′ 02″ | 4.37 | G2V | 5,847 | +0.24 | [8] |
半人马座α B | 14h 39m 35.0s | -60° 50′ 14″ | 4.37 | K1V | 5,316 | +0.25 | [8] |
蛇夫座70 A | 18h 05m 27.3s | +02° 30′ 00″ | 16.6 | K0V | 5,314 | –0.02 | [9] |
天龙座σ | 19h 32m 21.6s | +69° 39′ 40″ | 18.8 | K0V | 5,297 | –0.20 | [10] |
仙后座ηA | 00h 49m 06.3s | +57° 48′ 55″ | 19.4 | G0V | 5,941 | –0.17 | [11] |
双鱼座107 | 01h 42m 29.8s | +20° 16′ 07″ | 24.4 | K1V | 5,242 | –0.04 | [7][12] |
猎犬座β | 12h 33m 44.5s | +41° 21′ 27″ | 27.4 | G0V | 5,930 | -0.30 | [7] |
室女座61 | 13h 18m 24.3s | -18° 18′ 40″ | 27.8 | G5V | 5,558 | –0.02 | [5] |
杜鹃座ζ | 00h 20m 04.3s | –64° 52′ 29″ | 28.0 | F9.5V | 5,956 | –0.14 | [6] |
猎户座ψ¹ A | 05h 54m 23.0s | +20° 16′ 34″ | 28.3 | G0V | 5,902 | –0.16 | [7] |
后发座β | 13h 11m 52.4s | +27° 52′ 41″ | 29.8 | G0V | 5,970 | –0.06 | [7] |
HR 4523A | 11h 46m 31.1s | –40° 30′ 01″ | 30.1 | G5V | 5,629 | –0.29 | [5] |
大熊座61 | 11h 41m 03.0s | +34° 12′ 06″ | 31.1 | G8V | 5,483 | –0.12 | [7] |
HR 4458A | 11h 34m 29.5s | –32° 49′ 53″ | 31.1 | K0V | 5,629 | –0.29 | [5] |
HR 511 | 01h 47m 44.8s | +63° 51′ 09″ | 32.8 | K0V | 5,333 | +0.05 | [7] |
苍蝇座α | 06h 10m 14.5s | –74° 45′ 11″ | 33.1 | G5V | 5,594 | +0.10 | [6] |
网罟座ζ1 | 03h 17m 46.2s | -62° 34′ 31″ | 39.5 | G3-5V | 5,733 | -0.22 | [6] |
网罟座ζ2 | 03h 18m 12.8s | -62° 30′ 23″ | 39.5 | G2V | 5,843 | -0.23 | [6] |
巨蟹座55 | 08h 52m 35.81s | +28° 19′ 51″ | 40.3 | G8V | 5,235 | +0.25 | [11] |
HD 69830 | 08h 18m 23.9s | -12° 37′ 56″ | 40.6 | K0V | 5,410 | -0.03 | [6] |
HD 10307 | 01h 41m 47.1s | +42° 36′ 48″ | 41.2 | G1.5V | 5,848 | -0.05 | [7] |
HD 147513 | 16h 24m 01.3s | -39° 11′ 35″ | 42.0 | G1V | 5,858 | +0.03 | [5] |
波江座58 | 04h 47m 36.3s | -16° 56′ 04″ | 43.3 | G3V | 5,868 | +0.02 | [6] |
仙女座εA | 01h 36m 47.8s | +41° 24′ 20″ | 44.0 | F8V | 6,212 | +0.13 | [6] |
HD 211415 A | 22h 18m 15.6s | –53° 37′ 37″ | 44.4 | G1-3V | 5,890 | -0.17 | [6] |
大熊座47 | 10h 59m 28.0s | +40° 25′ 49″ | 45.9 | G1V | 5,954 | +0.06 | [6] |
天炉座αA | 03h 12m 04.3s | -28° 59′ 21″ | 46.0 | F6V | 6,275 | -0.19 | [6] |
巨蛇座φA | 15h 44m 01.8s | +02° 30′ 55″ | 47.9 | G5V | 5,636 | -0.03 | [7] |
HD 84117 | 09h 42m 14.4s | –23° 54′ 56″ | 48.5 | F8V | 6,167 | –0.03 | [6] |
HD 4391 | 00h 45m 45.6s | –47° 33′ 07″ | 48.6 | G3V | 5,878 | –0.03 | [6] |
小狮座20 | 10h 01m 00.7s | +31° 55′ 25″ | 49.1 | G3 V | 5,741 | +0.20 | [7] |
凤凰座ν | 01h 15m 11.1s | –45° 31′ 54″ | 49.3 | F8V | 6,140 | +0.18 | [6] |
飞马座51 | 22h 57m 28.0s | +20° 46′ 08″ | 50.9 | G2.5IVa | 5,804 | +0.20 | [6] |
孪生太阳
[编辑]这些恒星与太阳更为相似,它们要具备以下的性质[1]:
- 与太阳的温度差异小于50K(大约是5720至5830K)。
- 金属量为太阳的89—112% (± 0.05 dex),意味着这些恒星的原行星盘会有几乎同的尘埃量以形成行星。
- 没有恒星的伴星,因为太阳本身是孤独的。
- 与太阳的年龄差距在10亿年内(大约35亿至56亿)
以下是已知满足这些条件,最接近孪生太阳的恒星(太阳被列入以便进行比较):
恒星名称 | J2000座标[4] | 距离[4] (ly) |
恒星 分类[4] |
温度 (K) |
金属量 (dex) |
年龄 (十亿年) |
注解 | |
---|---|---|---|---|---|---|---|---|
赤经 | 赤纬 | |||||||
太阳 | — | — | 0.00 | G2V | 5,778 | +0.00 | 4.6 | [13] |
天蝎座18 | 16h 15m 37.3s | –08° 22′ 06″ | 45.1 | G2Va | 5,835 | +0.04 | 4.2 | [14] |
HD 44594 | 06h 20m 06.1s | -48° 44′ 29″ | 84 | G3V | 5,840 | +0.15 | 4.1 | [15] |
HD 150248 | 88 | G2 | 5,750 | -0.04 | 6.2 | [16] | ||
HD 164595 | 91 | G2 | 5,790 | -0.04 | 4.5 | [16] | ||
HD 195034 | 20h 28m 11.8s | +22° 07′ 44″ | 92 | G5 | 5,760 | -0.04 | 2.9 | [17] |
HD 117939 | 98 | G3 | 5,765 | -0.10 | 6.1 | [16] | ||
HD 138573 | 15h 32m 43.7s | +10° 58′ 06″ | 101 | G5IV-V | 5,750 | 0.0 | 5.6 | [18][16] |
HD 142093 | 15h 52m 00.6s | +15° 14′ 09″ | 103 | G2V | 5,841 | –0.15 | 1.3 | [18] |
HD 71334 | 124 | G2 | 5,710 | -0.06 | 5.1 | [16] | ||
HD 98618 | 11h 21m 29.1s | +58° 29′ 04″ | 126 | G5V | 5,851 | +0.03 | 4.2 | [14] |
HD 98649 | 137 | G3 | 5,775 | -0.02 | 4.7 | [16] | ||
HD 134664 | 140 | G3 | 5,820 | 0.13 | 2.6 | [16] | ||
HD 143436 | 16h 00m 18.8s | +00° 08′ 13″ | 141 | G0 | 5,768 | +0.00 | 3.8 | [18] |
HD 129357 | 14h 41m 22.4s | +29° 03′ 32″ | 154 | G2V | 5,749 | –0.02 | 8.2 | [18] |
HD 118598 | 160 | G2 | 5,755 | 0.02 | 4.3 | [16] | ||
HD 133600 | 15h 05m 13.2s | +06° 17′ 24″ | 171 | G0 | 5,808 | +0.02 | 6.3 | [14] |
HD 115382 | 176 | G1 | 5,775 | -0.08 | 6.1 | [16] | ||
Goromladen | 200 | G2V | 5,778 | 0.00 | 4.6 | |||
HD 101364 | 11h 40m 28.5s | +69° 00′ 31″ | 208 | G5V | 5,795 | +0.02 | 3.5 | [14][19] |
BD +15 3364 | 209 | G2 | 5,785 | 0.07 | 3.8 | [16] | ||
HD 197027 | 20h 41m 54.6s | -27° 12′ 57.4″ | 250 | G3V | 5,723 | -0.013 | 8.2 | [20] |
YBP 1194 | 08h 51m 00.807s | +11° 48′ 52.76″ | 2934 | G5V | 5,780 | +0.023 | 4.2 | [21] |
一些其他的恒星有时也会被题为孪生太阳的候选者,尤其是:常陈四(猎犬座β,请参阅Turnbull和Tarter)、双子座37 (参见Turnbull和Tarter)和天鹅座16 B(Porto de Mello et al. 2000)。然而,这三颗的温度和/或光度都太高了,不能成为真正的孪生太阳。而且,常陈四和天樽增一(双子座37)的金属量与孪生太阳相较也都太低。最后,奚仲四B(天鹅座16 B )是分离得很远的联星系统,并且要做为孪生太阳,年龄也太大了(至少已有70-80亿岁)。常陈四比较适合归类在前述的太阳相似体。
适居性
[编辑]孪生太阳的另一种定义是适居恒星 -一颗恒星的性质特别适合类似地球的行星。这些性质包括稳定性、质量、年龄、金属量和邻近的伙伴。
- 年龄至少30亿岁
- 位于在主序带上
- 是非变异性的恒星
- 拥有类地行星
- 支援动力学稳定的适居带
这需要恒星在主序带上停留的时间至少在30亿年以上,质量不能超过1.5倍的太阳质量,对应到最热的光谱型态为F5V。这样的恒星,在主序带的寿命结束时,绝对星等可以达到2.5等,或是太阳的8.55倍[22]。
在理想的情况下,非变异性是指变异性低于1%,但在实际上达到3%依然是可接受的范围内。一颗恒星的适居带会由于伴星与轨道的离心率,造成辐照度的变异,也是一个问题[22]。
在多星系统中的类地行星,由于含有三颗或更多恒星的系统,是不可能有长期稳定的轨道。在联星系统中,稳定的轨道是两种型式之一:S型(卫星或是拱星)轨道是环绕其中一颗恒星;和P型(行星或联星)轨道,环绕着整个联星系统。离心木星也可能干扰适居带中的行星轨道[22]。
金属量至少是太阳的40%([Fe/H] = -0.4)是形成类似地球的行星所必要的条件。高金属量与热木星的形成有着密切关联性,但这与生命无绝对的关系。像是一些气体巨行星最终有环绕着自己的轨道适居带,也可能有类似地球的卫星[22]。
相关条目
[编辑]参考资料
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进阶读物
[编辑]- G. W. Lockwood & B. A. Skiff. The Photometric Variability of Sun-like Stars: Observations and Results, 1984—1995. The Astrophysical Journal. 1997, 485 (2): 789–811. Bibcode:1997ApJ...485..789L. doi:10.1086/304453.
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