Comprehensive wavelengths and energy levels of Fe II, Cr II and other iron-group elements using Fourier transform

and grating spectroscopy

PI: Gillian NaveCo I: Craig J. Sansonet

National Institute of Standards and Technology, Gaithersburg, MD

NASA inter-agency agreement NNH10AN38I.

Start Date: January 2010.End Date: December 2012.

Objectives

1)Prepare a comprehensive linelist of about 15 000 lines in Fe II. Wavelengths from 90 nm to 5.5 µm. Wavelength uncertainty around 1:107. Identify lines using about 1000 energy levels with uncertainties of around 0.002 cm-1.

2)Prepare similar linelist for Cr II, containing over 4000 lines from 700 levels.

3)Record and analyze spectra of additional iron-group element, selected by consultation with astronomical community.

Research this year has focused on finishing Fe II and the UV/visible spectrum of Cr II.

High-resolution UV spectra from the Hubble Space Telescope

J. C. Brandt et al., AsJ 117, 1505 (1999)

Data for synthetic spectra require accurate wavelengths and oscillator strengths with comprehensive coverage for all elements and ionization stages

present in the stellar spectrum.

Background to objectives: Fe II

● Last major analysis of Fe II in 1978. Contained 3272 lines from 576 levels:

S. Johansson, “The spectrum and term system of Fe II,” Phys. Scr. 18, 217 (1978).● FT spectra of Fe-Ne and Fe-Ar hollow cathode lamps analyzed by G. Nave: Precise

wavelengths in Fe I published: 1991 and 1992.● Collaboration with S. Johansson (Lund Univ., Sweden) begun in 1992 – combined FTS

& grating spectra contain 34000 lines from 83 nm to 5.5 µm.● 9500 of these lines are Fe I:

G. Nave, S. Johansson, R. C. M. Learner, A. P. Thorne, J. W. Brault, “A new multplet table for Fe I,” ApJS, 94, 221 (1994).

● About 15000 are Fe II. Analysis begun by S. Johansson, but remained uncompleted when Johansson died in 2008.

Known energy levels of Fe II in 1978:doubly-excited system.

Known energy levels of Fe II in 1978:singly-excited system.

1978: 576 levels; 2011: 1085 levels

Increase in # lines over Johansson (1978)

High-excitation levels from HR6000

• 109 new levels from 3d6(3L)4f (L=P, H, F, G) found using UVSE spectra of HR600 & 46 Aql Castelli & Kurucz (A&A 520, A57 (2010))

• Majority of lines too high excitation to give lines in laboratory spectra, but some lines from these levels in lab

• Currently verifying which of the lines from these levels in lab spectra are correct.

• Calculations of Kurucz helpful, but not predictive.

• Are all levels correct?

Example comparison with Kurucz: FTS lines observed from 3d6(3P)4d 4F level at 104107.937 cm-1

Intensity FWHM Wavenumber Lower level

-1.04 24 83 12940.0002 -0.003-2.97 25 73 13037.3707 -0.005-1.84 12 72 13469.1117 -0.006-2.50 20 114 13620.1355 0.021-0.93 4 185 34501.3604 -0.014-1.25 6 224 39276.0125 0.022-1.99 11 204 40159.1370 0.0000.09 59 240 41418.0650 0.000

-0.76 11 271 41785.5093 0.0120.14 71 246 42024.8211 0.001

-0.85 10 329 42595.3178 0.010-0.66 11 257 43014.5369 0.003-1.71 7 217 43066.2427 0.038-1.84 3 208 43151.1168 -0.041-0.79 4 251 43300.6880 -0.009-0.87 8 175 43705.5968 -0.007-1.53 5 126 59323.1832 0.027

log(gf) obs-calc(10-3 cm-1) (cm-1) (cm-1)

(5D)5p 6P7/2

(5D)5p 4F5/2

(5D)5p 4D5/2

(5D)5p 6F5/2

(3G)4p y2F7/2

(a3F)4p y2G9/2

(a3F)4p y4G9/2

(a3P)4p y4D5/2

(3H)4p z2G7/2

(3H)4p z2G9/2

(3H)4p z4I9/2

(a3P)4p z2D5/2

(3H)4p z4G5/2

(3H)4p z4G7/2

(3H)4p z4G9/2

(a3P)4p y4P5/2

(5D)4p z4D5/2

Current status of Fe II

• Identifications for 13500 spectral lines in Fe II confirmed. About 500 have more than one identification.

• Verifying levels of Kurucz & Castelli – roughly 100 more lines.

• Need to add (5D)5g-6h lines (about 60 lines).

• Revise intensity scale?

• Aim to finish by end of 2011.

Sveneric Johansson’s last paper:

Background to research: Cr II

● Last major analysis of Cr II in 1951. Contained 1843 lines from 99 levels:

● C. C. Kiess, “Descripton and analysis of the second spectrum of chromium, Cr II,” J. Res. NBS 47, 385.

● ASD contains 743 levels, most of variable quality, unpublished with no published lines.

● Spectra of low-current Pt-Cr-Ne lamps taken at NIST for calibration of STIS using FTS and grating:

C. J. Sansonet, F. Kerber, J. Reader, M R. Rosa, “Characterizaton of the far-ultraviolet spectrum of Pt/Cr-Ne hollow cathode lamps as used on the space telescope imaging spectrograph on board the Hubble space telescope,” ApJ 153, 555 (2004).

These are the spectra being used in the current analysis. Will be combined with IR spectra of high-current hollow cathode lamp recorded using NIST 2-m FTS.

2-m FTSHigh Current HCL2.0 A2.0 Torr Ne Si photodiode

FT700 VUV FTSLow Current HCL20 mA ≈ 5.0 Torr NeR106UH PMTUG11 Filter

FT700 VUV FTSLow Current HCL20 mA≈ 5.0 Torr NeR1220 PMT

Current Status of Cr II Project

● Grating spectra recorded in region 1131 – 1844 Å

928 Cr II lines

● FTS spectra and measured in region 1568 – 4000 Å

2750 Cr II lines● FTS spectra recorded from 3000 – 11000 Å.● Energy levels optimization

3457 total classified lines

3361 used in level optimization

284 of 334 even levels optimized

347 of 369 odd levels optimized

Many level values change faroutside the estimated 0.05 cm-1

uncertainty of the levels from Sugar & Corliss

61% of optimized levels have uncertainties <0.005 cm-1. 91% have uncertainties <0.02 cm-1

• Chromium is more abundant in chemically peculiar stars than the sun.

• Ritz wavelength of the Cr II line 4848 Å agrees poorly with astronomical spectra. There is no precise laboratory wavelength for this line.

• From our optimized levels the Cr II 4848 Å line wavelength is 4848.2506(5) Å, an increase of 0.0156 Å from the original Ritz value.

Ryabchikova, unpublished

Future directions.

● Fe II to be finished by end of 2011.

● Cr II vis/UV finished soon, IR region to be measured and analyzed.

● Plan to start another singly-ionized element next year: Mn II?

1994 2010

Lab (full time) 3 1

Lab (part time) 0 1/4

Data compilations (full time) 2 3

Data compilations(part time)

3 4

NIST atomic spectroscopy groupThen and now

Other astronomy projects in NIST Atomic Spectroscopy Group

● Calibration of Pt/Ne hollow cathode lamps for GHRS (NASA-funded).

● Calibration of Pt/Cr/Ne hcls for STIS (NASA funded).

● Aging tests of Pt lamps for COS (NASA funded).

● Calibration of Th/Ar lamps in infrared (ESO/NASA funded) for CRIRES.

● Calibration of U/Ne lamps in IR (NRC postdoctoral project).

NASA funding essential to continuation of laboratory program in NIST Atomic Spectroscopy Group.