Ask a question, get an answer! This will eventually be a repository for posting outstanding IGRINS issues and questions, and getting answers.
Send all questions to kfkaplan@astro.as.utexas.edu
Q: How do I observe stars or point source objects?
A: IGRINS is optimized for observing stars, and they are the simplest types of objects to observe. Stars are placed in either position A or position B along the slit, and dithered between these two positions between exposures. Typically we take exposures in a sequence called a "quad" where you start at position A, take one exposure, move to position B, take two exposures, and then back to position A for one final exposure, resulting in an ABBA quad. The B positions are subtracted from the A positions such that B acts as the sky, bias, and dark subtraction for A and vice-versa. This way all exposures get signal from your science target, while simultaneously acting . The data reduction pipeline then fits the combined of A-B frames to optimally extract the signal for your science target.
Q: How do I observe extended source objects
A: Similar to piont sources (see question above), but you must dither your object ON and OFF the slit. A quad would look like ON-OFF-OFF-ON, similar to an ABBA quad but with ~1/√2 times the signal. The pipeline will subtract the OFF frames from the ON frames to account for sky, dark, and bias.
Q: I have a star or object of magnitude X and want to get a signal-to-noise of XX. How do I calculate my exposure times?
A: You can look at this chart and equation here for A0 type stars, derived from the ETC, and generally applies well to all stars. You can also calculate your own signal-to-noise estimates with the Exposure Time Calculator (ETC) which can be downloaded here. Note that Park et al. (2014; SPIE Proceedings) found that the S/N estimates from the ETC should be multiplied from the ETC by 0.83.