Radial velocity and line broadening in spectra. Dr. Katie Devine The College of Idaho SMSW2, 22 February 2019

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1 Radial velocity and line broadening in spectra Dr. Katie Devine The College of Idaho SMSW2, 22 February

2 Background hysics arleton College (Northfield MN) Astronomy niversity of Wisconsin (Madison) arly conditions of massive star orming environments nternal properties of infrared ark clouds College of Idaho hysics professor since 2009 ntro and upper division physics ntro astronomy Image credit: Milky Way Project (milkywayproject.org) Infrared dark clouds are seen in silhouette agai background glowing dust emission.

3 Research sive Star Formation adio: VLA, Green Bank Telescope nfrared: Spitzer, Herschel archical star formation ubbles ellowballs connection to this erence: I use radio spectral s to determine conditions of ecular gas in star forming s. Image credit: NASA/JPL-Caltech Milky Way Project volunteers first pointe yellowballs to researchers (2012).

4 ission and Absorption Lines (Spectral es) Fingerprints of atoms and molecule Images: Pearson e

5 Atoms and Absorption Lines: The usual model Absorption can boost an electron to the second (or higher) excited state Ways to decay: 1. To ground state 2. Cascade one orbital at a time Image: Pearson ed

6 ere are other ways generate emission es besides eating otons isional excitation: can be used to easure the density, mperature of gas Image:

7 dditional types of energy levels of atoms nd molecules Energy levels of the hydrogen atom: tron/proton spin alignments have ifferent energies. Example: 21 cm ne in hydrogen. Molecule s direction of rotat around its axis of symmet Example: position of N at ammonia (NH 3 ). Image: teachastronomy.com, readingfeynman

8 dio example: emission line CS C 34 S HC 3 N CH 3 OH V LSR (km/s) Devine et a

9 portant Features Intensity amount of energy collected per wavelength bin V LSR (km/s) Not a line has structure CS C 34 S HC 3 N CH 3 OH Molecular emissi Units of velocity, not wavelength

10 dial Velocity and Line Broadening Not a line has structure CS C 34 S HC 3 N CH 3 OH V LSR (km/s) Units of velocity, not wavelength

11 The Doppler Effect Light can t travel faster (or slower) than the speed of light, even if it is emitted from a moving source. If one is moving toward a source of radiation, the wavelengths seem shorter (higher energy photons); i moving away, they seem longer (lower energy photons). Image: Pearson ed

12 ends only on the relative ion of source and erver motion must be ial (towards or away line of sight) to cause pler Effect The Doppler Effect = v/c e shift = higher radial city Image: Pearson ed

13 adial velocity vs. source velocity dial velocity: use Doppler Shift Transverse velocity ( v T ) ansverse velocity: astrometry (if you can ) θ Source velocity ( v s ) v R = v s cos θ v S 2 = v R 2 + v T 2

14 Velocity in Our Galaxy: Galactic Rotation Radial velocity (relative to Sun) of gas in Milky Way spiral arms Image: NASA (APOD 25 A 2005)

15 Velocity in Our Galaxy: Galactic Rotation Radial velocity as tool to getting distances to objec in spiral arms ( We obtained source distance using a kinematic model Reid et al., ApJ, 2016

16 Gas in other galaxies Hydrogen in M33 (Triangulum or Pinwheel Galaxy) imaged by VLA and Westerbork telescopes. Image: NRAO, Image Credit & Copyright: Giovanni Beni (NASA APOD 2016 September 17

17 Velocities of other galaxies Edwin Hubble s observations of galaxies with the redshift in their spectral lines (1943). Expansion, motion within Galaxy clusters, rotation o galaxies

18 Planetary Rotation Example: Rotation of Ju Image: Shelyak.com

19 H F P-Cygni Profiles Bottom shows the continuum from star with absorption in front (F) an emission from halo (H) Image: Figure 2.4 from Lamers & Cassinelli, Introduction to Stellar Wi 1999, Cambridge University Press

20 dial Velocity and Line Broadening Not a line has structure CS C 34 S HC 3 N CH 3 OH V LSR (km/s) Units of velocity, not wavelength

21 e Broadening Dispersion: Natural broadening Pressure broadening Gaussian: Thermal Turbulence See David Whelan s talk for more!

22 ocity of Individual Atoms: Statistical sics is fraction of atoms with velocity between v and v+dv Image credit:

23 ocity of Individual Atoms: Statistical sics )dv is fraction of atoms with ity between v and v+dv )dv is probability distribution epends on gas properties bility distribution determines e shape Image credit:

24 ocity of Individual Atoms: Statistical sics )dv is fraction of atoms with ity between v and v+dv )dv is probability distribution epends on gas properties bility distribution determines e shape Maxwell-Boltzmann distribution ideal g with random motions

25 ocity of Individual Atoms: Statistical sics )dv is fraction of atoms with ity between v and v+dv )dv is probability distribution epends on gas properties bility distribution determines e shape Cauchy Lorentz (Lorentzian) distribution homogeneous broadening Image credit:

26 ocity of Individual Atoms: Statistical sics axwell-boltzmann distribution: ermal (Doppler) broadening Lorentz distribution: Natural (uncertainty principle) broadeni Collisional broadening

27 ocity of Individual Atoms: Statistical sics Voigt profile: convolution of Gaussian and Lorentzian profiles Figure: Huang & Yung, A Common Misunderstanding about the Voigt Line Profile 2003 Journal of The Atmospheric Sciences

28 xample: Thermal Motion emperature is Energy, Energy is Motion T= 2/3 KE avg / k b k b is Boltzmann s constant, 1.38 x10-23 Rearrange to get average kinetic ener of a gas: KE avg = 3/2 k b T= 1/2 m v average 2 ttp://web.mit.edu/16.unified/www/fall/thermodynamics/thermo_4.htm

29 rmal Linewidths ing gas random motions follow Maxwellann distribution: (v)= ( m/2πkt ) 3 4π v 2 exp [ m v 2 /2kT ] FWHM= 1/λ 8 k T/m ln 2 Image credit: spectral line broadening via BotReje at

30 elocity in Gas: Turbulent motion Stars, Gas, and Dust Battle the Carina Nebula Image Credit & Copyright: Bastien Fouch NASA APOD 2017 August 15 Measure the temperature of a gas, and find that lines are broader than thermal linewidthsà there is probably turbulent motion

31 un science example: using spectra to ok for evidence of in-falling clouds Watson, Devine et al. 2016: CS lin profiles show evidence of infall Infall model: Myers et al , b) N90-2 and c) N Cartoon: J. M

32 science example: using spectra to mine motion of gas in clouds km/s 52.8 km/s 53.4 km/s CS (1-0) central velocit image of N65. White outline shows region pped in CS (1-0). Watson et al. 2016

33 science example: using line profiles nterpret Be Star spectra Rivinius, Carciofi & Martay

34 ummary Origin of emission/absorption spectra, conditions for each (Kirchhoff s Laws) Doppler shift, and how to convert from wavelength to line-of-sight velocity Bulk motions of gas: galactic rotations, galactic motion, planetary rotation Motion within gas and line broadening, thermal vs. turbulent motion Science examples: using line profiles to probe star formation, dense gas conditions, stellar atmospheres

35 eview: Sources of Emission simplified version) Images: Pearson educ Shelyak Instruments (

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