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Absorption spectra of interstellar clouds Jacek Krełowski Centrum Astronomii UMK, Toruń, Poland Instytut Fizyki Toretycznej i Astrofizyki UG

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Presentation on theme: "Absorption spectra of interstellar clouds Jacek Krełowski Centrum Astronomii UMK, Toruń, Poland Instytut Fizyki Toretycznej i Astrofizyki UG"— Presentation transcript:

1 Absorption spectra of interstellar clouds Jacek Krełowski Centrum Astronomii UMK, Toruń, Poland Instytut Fizyki Toretycznej i Astrofizyki UG

2 Collaborators: Gazinur A. Galazutdinov Bohyunsan Optical Astronomy Observatory, Jacheon, YoungChun, KyungPook, , South Korea Faig A. Musaev Special Astrophysical Observatory, Nizhnyi Arkhyz, Russia Arkadij Bondar International Centre for Astronomical and Medico-Ecological Research, Terskol, Russia Andrzej Strobel Torun Center for Astronomy, Nicolaus Copernicus University Piotr Gnaciński Institute of Theoretical Physics and Astrophysics, Gdańsk University Andrzej Megier Torun Center for Astronomy, Nicolaus Copernicus University

3 „A hole in the sky” – absorbing interstellar cloud among stars in the Milky Way

4 Absorption spectral features originating in interstellar clouds Atomic lines from ground levels (known since 1904) Features of simple molecules (known since 1937) Diffuse interstellar bands (known since 1922) CaII, NaI, KI, CaI and LiI (vis.) Others – far-UV (Copernicus, IUE, HST) Polar species: CH, CH +, CN, CO Homonuclear ones: H 2, C 2, C 3 Unidentified ; Proposed carriers: carbon chains, PAHs, fulleranes

5 Basic, simple questions: E B-V => A V ? Are the carriers of interstellar absorptions well mixed (spatially correlated)? Are the strengths of interstellar absorptions related to the total column density of hydrogen? Are physical parameters of different environments similar?

6 CaII lines as seen in a reddened star spectrum

7 „H” line of the same doublet; the orbital period of oPer is 4.5 days

8 Extreme narrowness of the interstellar CaII line caused by the low density of the medium (observed at Pic du Midi and Terskol)

9 Weak and thus rarely observed CaI line in the spectra of two heavily reddened stars; R=120,000

10 Sodium dublet D 1 and D 2 discovered by Heger in 1919 – the lines are usually saturated

11 Doublet of neutral potassium; the feature near 7665 A is usually blened with telluric ones. Here both lines clearly seen in two BOE spectra

12 Neutral iron lines seen in ultraviolet

13 Very weak line of neutral interstellar Lithium; spectra from BOE spectrograph

14 The extremely weak line of neutral interstellar rubidium

15 Oxygen, sulphur and phosphorus in HST spectra taken with high resolution

16 A vast majority of atoms in the Universe (90%) are hydrogen atoms but...

17 Not either a weakest sign of interstellar H  absorption can be traced – here two heavily reddened objects; MAESTRO R=120,000

18 Analysing interstellar atomic lines we arrive at some conclusions... A vast majority of IS atomic lines (resonant ones) can be observed only if using space-born instruments; this follows the extremely low density of ISM Many of the elements are heavily depleted; only no more than of their cosmic abundance is observed in interstellar gas (Fe, Ni, Mg etc.) Young stars do not show the above depletions; the „lost” elements must be present in IS dust grains

19 The first IS molecular stationary line – of CH radical seen towards the spectroscopic binary oPer;

20 Very narrow profile of the polar CH radical observed at CFHT (R=32,000) and at Terskol (R=120,000)

21 Variable physical conditions in interstellar clouds: neighbour features of CaI and CH +; ( spectra from Terskol, R=120,000)

22 Sequence of interstellar molecular features; note the variable CN/CH strength ratio

23 Different rotational CN temperatures towards two reddened stars; Gecko high res.

24 Observations of H 2 close to the Lyβ line using the FUSE satellite

25 The strongest (Mullikan) band of C 2 homonuclear molecule in the HST high res. spectrum

26 Phillips (2,0) band of C 2 molecule in near infrared (BOE and Terskol)

27 The band of C 3 molecule observed with the aid of 3.6m telescope at ESO (spectrograph CES, resolution R=220,000)

28 Interstellar KI line evidently Doppler- splitted; the medium is not homogeneous

29 Radial velocities of different species are not identical; here the R=120,000 Terskol spectrum

30 Different species may be originated in different clouds; BOE spectrum

31 What do the profiles of interstellar features tell us? Lines of sight toward most of OB stars intercept more than one cloud Strength ratios of Doppler components are different in different features Radial velocities measured in different observed features may be different It is thus difficult to determine rest wavelengths of features which remain unidentified – like diffuse interstellar bands

32 Doppler dance of stellar lines in the spectroscopic binary oPer; sodium doublet and diffuse bands are stationary (spectra from BOES )

33 Very broad 6170 DIB, two strong ones and a „forest” of very weak and narrow features; HD (red line), BD (blue line)

34 Strong and weak diffuse interstellar bands in the spectroscopic binary οPer

35 High resolution (R=120,000) profiles of two narrow DIBs compared to that of CH feature in ζPer

36 Variable strength ratio of the major DIBs; spectra R=32,000 from CFHT

37 Examples of strength ratios of molecular features and the major DIBs

38 Narrow DIBs share the Doppler splitting of the CH 4300 line in the spectrum of BD

39 Details of the 5797 DIB profile observed in ultra high resolution

40 Variable profile of the 6196 DIB in spectra from ESO, R=220,000, S/N~1000

41 Substructures in profiles of weak DIBs – spectra from Gecko

42 Interstellar features may be formed in different clouds along the same sight-line

43 Narrow IS features in the same object as above but R=120,000 (Terskol)

44 Correlation between trigonometric parallax and CaII „K” line (D=2.78EW(K)+98 (pc)

45 Correlation between trigonometric parallax and CaII „H” line (D=4.58EW(H)+102 (pc)

46 Absolute magnitudes of two B1I stars, estimated using H and K distances

47 Print this page Next article page

48 Neutral potassium does not correlate with distance. The same sample as in the former slide.

49 The absorption feature of CH (4300 A) does not correlate with trigonometric parallax

50 The major 5797 diffuse band does not correlate with the trigonometric parallax

51 The lack of correlation between E(B-V) and distance

52 Different radial velocities and profiles of various interstellar lines (R=120,000)

53 Very tight correlation between column density of H 2 and equivalent width of CH 4300 Ǻ line

54 E(B-V) colour excess is very well correlated with the line strength of CH radical

55 Red-shift of DIBs in the spectrum of HD37061

56 Blue-shift of diffuse band in the spectrum of AE Aur (HD34078)

57 But the abundance of the homonuclear C 2 molecule does not correlate with E(B-V)

58 As well as that of CN...

59 What do correlations between interstellar lines tell us? The space is filled with clouds dominated with HII, HI and/or H 2 depending on physical conditions; many sightlines intercept all kinds of clouds Interstellar medium is quite evenly filled with HII clouds revealed by the CaII H and K lines, HI and H 2 clouds are much smaller geometrically but evidently denser; best correlated carriers should occupy smallest, homogeneous clumps Proper motion of dense clumps may lead to some variability of interstellar features

60 High S/N profiles of 6614 DIB observed in the same spectra during the same nights; HD is binary

61 Where do originate different interstellar spectral features: The environment of HI clouds is most likely populated with the carriers of broad 5780 i 6284 diffuse bands. Dense H 2 clouds contain the carriers of KI, CH, 5797, E(B-V); note that H 2 molecules are formed on grains Vast HII clouds of low density and high ionization rate are revealed by the CaII H and K doublet Where CH + is located? Hard to say.

62 Some conclusions... Strength of CaII lines is quite tightly correlated with distance. They allow to measure distances of OB stars with a reasonable precision Division of the observed features into the spectra of HII, HI and H 2 clouds allows to describe the spectra of single, homogeneous clouds Measurements of EW(CH) allow to estimate E(B-V) and N(H 2 ) with the precision comparable to the traditional methods

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