光度函數 (天文學)
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關於光度學的光度函數，請見“
光度函數”。
光度函數在天文學上為恆星或星系的光度分佈[1]，是用來研究數量龐大的族群或類別的性質，像是星團中的恆星或是星系團中的星系。
謝克光度函數
謝克光度函數給出了以光度為變數的星系空間密度函數，其型式是：
- n(x) dx=ϕ∗xae−xdx,displaystyle n(x) mathrm d x=phi ^*x^amathrm e ^-xmathrm d x,
此處x=L/L∗displaystyle x=L/L^*
，L∗displaystyle L^*
是星系的特徵光度，決定函數中冪律的適用範圍。ϕ∗displaystyle ,!phi ^*
是歸一化常數，單位是數量密度。星系的光度函數在不同的族群和環境中可能會有不同的參數，它不是一個通用的函數。一個從場星系的測量中的估計是 a=−1.25, ϕ∗=1.2×10−3h3Mpc−3displaystyle a=-1.25, phi ^*=1.2times 10^-3h^3mathrm Mpc ^-3
。[2]
為了方便，謝克光度函數常被改寫成以星等為變數，並有以下形式；
- n(M) dM=0.4 ln10 ϕ∗[100.4(M∗−M)]α+1exp[−100.4(M∗−M)] dM.displaystyle n(M) mathrm d M=0.4 ln 10 phi ^*[10^0.4(M^*-M)]^alpha +1exp[-10^0.4(M^*-M)] mathrm d M.
![displaystyle n(M) mathrm d M=0.4 ln 10 phi ^*[10^0.4(M^*-M)]^alpha +1exp[-10^0.4(M^*-M)] mathrm d M.](https://wikimedia.org/api/rest_v1/media/math/render/svg/154794b18f5316e38d53502ca68a0b965b989a4c)
注意到因為星等是對數形式，冪律有著對數斜率α+1displaystyle alpha +1
。這就是為什麼α=−1displaystyle alpha =-1
的謝克光度函數是平的。
白矮星光度函數
白矮星光度函數 (white dwarf luminosity function，WDLF) 給定白矮星的數量和光度。當在測量這類恆星的形成和冷卻的速率時，它提供有價值的資訊，像是白矮星冷卻的物理和年齡，以及星系的歷史[3][4]。
參考資料
^ Stahler, S.; Palla, F. The Formation of Stars. Wiley VCH. 2004. ISBN 9783527618675. doi:10.1002/9783527618675.
^
Longair, Malcolm. Galaxy Formation. Springer-Verlag. 1998. ISBN 3-540-63785-0.
^ The Texas Deep Sky Survey: Spectroscopy of Cool Degenerate Stars, C. F. Claver, D. E. Winget, R. E. Nather, and P. J. MacQueen, Bulletin of the American Astronomical Society 30 (December 1998), p. 1300
^ The Potential of White Dwarf Cosmochronology, G. Fontaine, P. Brassard, and P. Bergeron, Publications of the Astronomical Society of the Pacific 113, #782 (April 2001), pp. 409–435.
白矮星
|
|---|
| | 形成 | - 錢德拉塞卡極限
- PG 1159星
- 恆星演化
- 赫羅圖
- 米拉變星
|
|---|
| | 宿命 | - 黑矮星
Ia超新星
中子星
恆星黑洞
致密星
- 臨終氦星
- B型次矮星
- 氦行星
|
|---|
| | 双星系统 |
新星
- 矮新星
- 共生變星
激變變星
X射線聯星
聯星脈衝星
- 氦閃
- 碳引爆
|
|---|
| | 屬性 | |
|---|
| | 相關的 |
行星狀星雲
大质量重子天体强关联星团(RAMBOs)
- 白矮星光度函數
- 白矮星、中子星和超新星年表
|
|---|
| | 著名的 | - 范馬南星
- 天狼星B
- 南河三B
- 波江座40 B
- BPM 37093
- HL金牛座76
- 蛇夫座RS
|
|---|
| |
|
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關於光度學的光度函數，請見“光度函數”。
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