  Young stars are surrounded by copious amounts of circumstellar material. Its
composition, in particular its gas-to-dust ratio, is an important parameter.
However, measuring this ratio is challenging, because gas mass estimates are
often model dependent. X-ray absorption is sensitive to the gas along the
line-of-sight while optical/near-IR extinction depends on the dust content.
Therefore, the gas-to-dust ratio of an absorber is given by the ratio between
X-ray and optical/near-IR extinction. We present three systems where we used
X-ray and optical/near-IR data to constrain the gas-to-dust ratio of
circumstellar material; from a dust-rich debris disk to gaseous protoplanetary
disks.
