Atomic Spectroscopy for Space Applications: Galactic Evolution l M. P. Ruffoni, J. C. Pickering, G. Nave, C. Allende-Prieto

APOGEE is one of 4 instruments forming the third Slone Digital Sky Survey (SDSS3) It will conduct a spectroscopic survey of all stellar populations in the Milky Way It will measure in the near-IR where galactic dust extinction is ~1/6 of that at visible wavelengths It will measure chemical abundances and radial velocities of 100,000 evolved stars to help explain galactic evolution DurationSpring 2011 to Summer 2014 Spectra Measuring 1.51µm <  < 1.7µm Resolving power ~30,000 S/N Ratio greater than 100 Targets100,000 evolved stars 15 elements - Fe most important PrecisionMetal abundances to ~0.1 dex Radial velocities to <0.3 km s -1

Detecting elements in stars Photosphere Hot, dense interior Emission contains absorption lines Section of a star Visible spectra for different star types Absorption lines indicate the presence of an element. Line strength is mainly linked to: Stellar properties (e.g. temperature) Absorption transition probability Chemical abundance TemperatureType Simulated H-band spectrum for different Fe abundances. All other parameters fixed. Finding chemical abundances 1)Use a  2 fit to stellar models to obtain Stellar temperature Surface gravity Microturbulence parameter Abundance of important elements [Fe/H], [C/H], and [O/H] 2)Fix these then fit other abundances The results are only as good as the model!

Measuring Transition Probabilities E2E1E2E1  A 21 B 12 B 21 Einstein coefficients Spontaneous AbsorptionStimulated Emission Emission Transition probabilities can be obtained from emission spectra Number of experimentally measured transition probabilities in the IR: J. C. Pickering et al. Can J Phys 89 pp. 387 (2011) ScTiVCrMnFeCoNiCuZn –457–2651–4–1 Better experimental transition probabilities are needed

Decay to a single level Decay to multiple levels E2E1E2E1 E2E1E2E1 I I I I 12 Branching Fractions 12 BF = Branching fraction I = Integrated line intensity

Complications Spectrometer Response Determined by measuring a calibrated continuum source Tungsten lamp (IR to UV) Deuterium lamp (UV and vacuum UV) I I Normalised response Wavenumber / cm Normalised Response W lamp D 2 Lamp Free spectral range Spectral range determined by Spectrometer optics Detector sensitivity Filter combinations Measurement electronics Either Select range to measure all upper level branches or Use overlapping spectra to carry calibration

Measuring Upper Level Lifetimes Lifetimes are commonly measured with Laser Induced Fluorescence (LIF) E2E1E2E1 1)A laser pulse is used to excite electrons in a populated lower level. 2)The upper level is populated 3)After time the electrons de-excite Critical Fe I transitions for the APOGEE project There are no transitions to populated lower levels No lines in the visible/UV LIF lifetimes are unavailable BFs are unavailableNo lines to carry intensity calibration Wavenumber / cm Normalised Response nm UV - visible

Catch-22: Branching fractions or level lifetimes Situation BF 21 22 All lines in the IR At least 1 line in vis/UV Critical Fe I transitions for the APOGEE project Solution: Invert the problem

Solution: Invert the Problem Line strength is mainly linked to: Stellar properties (e.g. temperature) Absorption transition probability Chemical abundance Recall from slide 2 APOGEE needs transition probabilities to find abundances The Solar Fe abundance is known. Use it to find transition probabilities Estimate  2 from theory Use Solar spectrum to refine A 2i

Results A section of our results table:

Consistency Checking Relative transition probabilities can be found by combining absorption and emission data (Ladenburg 1933). Ratio of line strengths in emission: Ratio of line strengths in absorption: A 2i A 2j B 2j B 2k Lifetimes not needed

Results A section of our results table:

1)We have found a reliable method for obtaining IR transition probabilities 2)Present study has almost doubled the number of Fe transition probabilities available in the IR. 3)We have the data to quickly provide many more transition probabilities Conclusions Number of experimentally measured transition probabilities in the IR: J. C. Pickering et al. Can J Phys 89 pp. 387 (2011) ScTiVCrMnFeCoNiCuZn –457–2651–4–1 For more information: Technique: M. P. Ruffoni, Comp. Phys. Comm., accepted (2012) Results for APOGEE: M. P. Ruffoni et al., ApJ, submitted (2013) Results for GaiaESO: M. P. Ruffoni et al., ApJ, in preparation (2013)