Spectral energy distributions are presented for 94 young stars surrounded by disks in the Serpens Molecular Cloud , based on photometry and Spitzer IRS spectra .
Most of the stars have spectroscopically determined spectral types .
Taking a distance to the cloud of 415 pc rather than 259 pc , the distribution of ages is shifted to lower values , in the 1 – 3 Myr range , with a tail up to 10 Myr .
The mass distribution spans 0.2 – 1.2 M _ { \odot } , with median mass of 0.7 M _ { \odot } .
The distribution of fractional disk luminosities in Serpens resembles that of the young Taurus Molecular Cloud , with most disks consistent with optically thick , passively irradiated disks in a variety of disk geometries ( L _ { { disk } } / L _ { { star } } \sim 0.1 ) .
In contrast , the distributions for the older Upper Scorpius and \eta Chamaeleontis clusters are dominated by optically thin lower luminosity disks ( L _ { { disk } } / L _ { { star } } \sim 0.02 ) .
This evolution in fractional disk luminosities is concurrent with that of disk fractions : with time disks become fainter and the disk fractions decrease .
The actively accreting and non-accreting stars ( based on H \alpha data ) in Serpens show very similar distributions in fractional disk luminosities , differing only in the brighter tail dominated by strongly accreting stars .
In contrast with a sample of Herbig Ae/Be stars , the T Tauri stars in Serpens do not have a clear separation in fractional disk luminosities for different disk geometries : both flared and flat disks present wider , overlapping distributions .
This result is consistent with previous suggestions of a faster evolution for disks around Herbig Ae/Be stars .
Furthermore , the results for the mineralogy of the dust in the disk surface ( grain sizes , temperatures and crystallinity fractions , as derived from Spitzer IRS spectra ) do not show any correlation to either stellar and disk characteristics or mean cluster age in the 1 – 10 Myr range probed here .
A possible explanation for the lack of correlation is that the processes affecting the dust within disks have short timescales , happening repeatedly , making it difficult to distinguish long lasting evolutionary effects .