BC03

• AIR 波长，SDSS的谱是真空波长

AIR = VAC / (1.0 + 2.735182E-4 + 131.4182 / VAC^2 + 2.76249E8 / VAC^4)

AIRTOVAC可转换

• 3323-9301是高分辨率，1A

• As noted by Asari et al. (2007), the Bruzual & Charlot (2003) models have a low amplitude hump in the ∼100 Å interval around

Hβ, such that Hβ emission often sits in a slightly negative valley in the observed minus model spectrum (an artefact of the STELIB library, which disappears when using models based on the MILES library of Sanchez-Bl ´ azquez et al. 2006). Asari et al. (2007) found ´ this effect to be unimportant for their Hβ measurements, but their analysis focused on SF galaxies, which tend to have strong Hβ. Here it has a larger impact, since we are specifically interested in galaxies with intrinsically weak Hβ. To alleviate this problem, the Hβ flux measurements were performed with respect to a local ‘continuum’ in the residual spectrum. No such systematic residual is found for other emission lines, whose measurement does not require the extra care devoted to Hβ.