Spectral Typing Using TiO Bands

Reid et al. 1995:

• compare spectra to template spectra of known spectral type
• MMK System (Morgan et al. 1943)
• no late M-type spectral templates in MMK system
• KHM system (Kirkpatrick 1992)
• uses spectral features in the wavelength range 6300-9000 A
• Reid et al. 1995
• TiO bandheads at 6500A and 7050 A
• CaOH and CaH bands at 6250 and 6400/6800
• TiO band is temperature dependent
• can be used as a distance indicator (spectrophotometric parallax)
• "index" is defined as : R=F(W)/F(cont)
• F(cont) is the pseudocontinuum flux (e.g. mean flux in a sideband)
• Figure 1 from Reid et al. shows the spectrum of a typical mid-M star with the bands used for spectral typing indicated:

• They derive a direct (linear) relationship between the spectral number (M #), and the TiO index: Sp = -10.775*TiO5 + 8.2

THE PROBLEM:

Since my Kast spectra do not include the features near the TiO bandhead (due to the maximum grating tilt allowed by the telescope), I need to find a way to define spectral types based on the TiO1 band head. Hopefully these will agree with the spectral types quoted by Rodriguez et al. 2011, which were derived using broadband photometry. 

The Write-Up

I'm just starting to work on the write-up (which will hopefully turn into a publishable paper) on my observations of low mass stars over 5 months with the Lick 3-m telescope and a combination of the Hamilton Echelle Spectrometer and the Kast Dual Spectrometer.

First comes The Big Table, for which I need measured equivalent widths for H-alpha and Li. So I need to go back over all my old data and re-calculate my EWs to make sure I still agree with myself. One of our undergrads (Nicole Arulanantham) has already done this for our August data. Our method is to plot the spectra using IRAF's splot package, then measure the equivalent width using a Voigt profile fit (hit k, then v on either side of the line, making sure to include the flux in the wings). We do this a few times (~5) and take the average. This is because there is some intrinsic error in the calculation - the EW will depend on where you place the continuum level (where you cut off the wings).

Kast Observations, May 21 2013

While the weather has been looking good all day for tonight's run, the marine layer has moved in:

Courtesy of Pavl Zachary:

While it's pretty, it doesn't bode well for observing tonight. Humidity's up near 90%, which means we're teetering on the edge of closing the dome.

Calculating Rotational Velocities (vsini)

Now that I have a library of echelle spectra, I can measure rotational velocities for those stars without measurements in the literature.

To calculate rotational velocities from our Hamilton Echelle spectra, we will use the following technique from Fekel 1997:

Kast Observations, May 2013 (Night 3)

Tonight we will be focusing on our dimmer stars (Vmag~13-14), and thus will be observing fewer targets. It looks like we're going to have a full 4 nights of fair-weather observing (practically unheard of at Lick!). Tonight's seeing is ~0.7 arcseconds.

Kast Observations, May 2013 (Night 2)

Tonight, in addition to our own targets, we will be observing the AGN Zw 229-015 (AGN = Active Galactic Nucleus). By taking spectra using the Lick 3m telescope, the AGN team (Aaron Barth et al.) will be able to measure the Hbeta emission. This will help them to determine the mass of the black hole at the center of this AGN via a technique called reverberation mapping. 

Kast Observations, May 2013 (Night 1)

Our group has been granted 4 nights on the Shane 3m telescope at Lick Observatory on Mount Hamilton using the Kast Dual Spectrometer. Tonight we are observing a set of low-mass stars with little to no data in the literature to look for Ha in emission and strong lithium absorption (both signatures of youth). We can also look at the TiO bands (~7200 Angstroms) to get a better estimate of the spectral type.