Astropy

astropy.io.fits

[1]

>>> hdulist = fits.open('input.fits')
>>> hdulist.info()

header

• each element of an HDUList is an HDU object with .header and .data attributes, which can be used to access the header and data portions of the HDU.

>>> hdulist[0].header['targname']

• To see the entire header as it appears in the FITS file (with the END card and padding stripped), simply enter the header object by itself, or print(repr(header)):
• It’s also possible to view a slice of the header:

>>> header[:2]

• Another way to either update an existing card or append a new one is to use the Header.set() method:

>>> prihdr.set('observer', 'Edwin Hubble')

fits table 的读与写

• 写

from astropy.table import Table
t=Table([Bage,fzbin,Age_weight2],names=('Age','z','weights'))
t.write('SFH_LMC3_out.fits',format='fits')

• 读

hdu = fits.open('SFH_LMC3_out.fits')
hdu.info() #看看哪些hdu
data=hdu[1].data
data.columns #看看有那些列
Bage=data.field('Age')

fits文件打开过多错误

• [2]
• fits.close()
• 可能还根系统设置有关

ulimit -a
ulimit -n 100000
vim /etc/security/limits.conf

• 把python的软限制编程硬限制,参见 [3],下面方法貌似也不管用

import resource
soft, hard = resource.getrlimit(resource.RLIMIT_NOFILE)
resource.setrlimit(resource.RLIMIT_NOFILE, (hard, hard))

• lsof -p 进程id > openfiles.log命令，获得当前占用句柄的全部详情进行分析
• 实测这两个效果不好（python 3.8）

• del hdu.data
• hdu = fits.open(fits_name,memmap=False) #打开fits文件数目比较多的情况下

fits image读写

n = np.arange(100.0) 
hdu = fits.PrimaryHDU(n)
hdu.writeto('new2.fits')
hdu.writeto('new2.fits')

• 如果超过一个hdu

>>> hdul = fits.HDUList([hdu])
>>> hdul.writeto('new1.fits')

astrometry

• match 两个星表

>>> from astropy.coordinates import SkyCoord
>>> from astropy import units as u
>>> c = SkyCoord(ra=ra1*u.degree, dec=dec1*u.degree)  
>>> catalog = SkyCoord(ra=ra2*u.degree, dec=dec2*u.degree)  
>>> idx, d2d, d3d = c.match_to_catalog_sky(catalog)
>>> sel=np.where(d2d.degree < 0.00002)

宇宙学

http://docs.astropy.org/en/stable/cosmology/

• 从红移到年龄

>>>from astropy.cosmology import FlatLambdaCDM 
>>>cosmo = FlatLambdaCDM(H0=70, Om0=0.3)

>>> lum_dis=cosmo.luminosity_distance(redshift) #计算光度距离

• 从年龄到红移

>>> import astropy.units as u
>>> from astropy.cosmology import  z_at_value
>>> z_at_value(cosmos.age, 2 * u.Gyr)

单位转换

dL=lum_dis.to(u.cm)