Absorption spectra of interstellar clouds

Jacek Krełowski

Centrum Astronomii UMK, Toruń, Poland

Instytut Fizyki Toretycznej i Astrofizyki UG

www.astri.uni.torun.pl/~jacek

Collaborators:

Gazinur A. Galazutdinov

Bohyunsan Optical Astronomy Observatory, Jacheon, YoungChun, KyungPook, 770-820, 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

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

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: H2, C2, C3

Unidentified;

Proposed carriers: carbon chains, PAHs, fulleranes

Basic, simple questions:

EB-V => AV ?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?

CaII lines as seen in a reddened star spectrum

3940 3960 3980

0.3

0.6

0.9

CaII"K"

Rel

ativ

e in

tens

ity

Wavelength

HD 149038

CaII"H"

CH+

HI

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

3969 3972 3975

0.6

0.8

1.0

H

HD 23180; 25 and 28 Oct. 2001

Spectra of R=120,000 from Terskol echelle spectrometer

Rel

ativ

e in

ten

sity

Wavelength

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

3927 3930 3933

0.6

0.8

1.0

HD 24398

R=120,000 (MAESTRO)

R=32,000 (Musicos)

stellar features

CaII K

Re

lativ

e in

tens

ity

Wavelength

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

4225 4226 4227 4228

0.90

0.96

1.02

HD 207198

HD 210839

CaI

Rel

ativ

e in

tensi

ty

Wavelength

Sodium dublet D1 and D2 discovered by Heger in 1919 – the lines are usually saturated

5889 5892 5895 5898

0.0

0.4

0.8

Interstellar sodium dublet, Terskol Observatory, R=120,000

HD 24398

D2 D

1

Rela

tive in

ten

sit

y

Wavelength

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

7670 7680 7690 7700

0.0

0.6

1.2

Potassium doublet in the spectra of two reddened stars

HD 208501

HD 23180

Rel

ativ

e in

tens

ity

Wavelength

Neutral iron lines seen in ultraviolet

-60 -30 0 30 60

0.95

1.00

1.05

R=120,000Terskol Obs.

Neutral iron interstellar lines in HD 23180

FeI 3719.937 A

FeI 3859.913 A

Rel

ativ

e in

tens

ity

Radial velocity

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

6706 6708 6710

0.98

1.00

1.02

1.04

R

elat

ive

inte

nsity

Wavelength

HD204827

BD +40 4220

BD +60 594

LiI

The extremely weak line of neutral interstellar rubidium

7796 7800 7804

0.992

1.000

1.008

RbI interstellar line in averaged spectra from two spectrographs

RbI

MAESTRO spectrograph, R=120,000

BOE spectrograph, R=30,000

Rel

ativ

e in

tens

ity

Wavelength

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

1302 1303 1304

0.0

0.4

0.8

Oxygen dublet in far-UV HST spectrum of XPer

OIOI

SI

PII

PII

Rel

ativ

e in

ten

sity

Wavelength

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

Not either a weakest sign of interstellar H

absorption can be traced – here two heavily reddened objects; MAESTRO R=120,000

4855 4860 4865

0.7

0.8

0.9

1.0 H lab.

HD 207198

HD 210839

Rel

ativ

e in

ten

sity

Wavelength

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 ISMMany of the elements are heavily depleted; only no more than 0.001 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

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

4280 4300 4320

0.90

0.99

1.08

2004/02/12

Rel

ativ

e in

tens

ity

Wavelength

2004/02/09

CHHD 23180

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

4299.6 4300.0 4300.4 4300.8 4301.2

0.80

0.88

0.96

Per

CH

Terskol R=120,000

PdM R=32,000

Rel

ativ

e in

tens

ity

Wavelength

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

4227 4230 4233

0.8

0.9

1.0

1.1

HD24912

HD207198

CH+

CaI

Rel

ativ

e in

tens

ity

Wavelength

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

3876 3882 3888

0.8

1.0

1.2 HD 34078

HD 179406

CH

CH

CH

CN

CNCN

Rel

ativ

e in

tensi

ty

Wavelength

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

3873 3874 3875 3876 3877

0.6

0.8

1.0

Gecko/CFHT

HD 208501

HD 206165

Rel

ativ

e in

tens

ity

Wavelength

Observations of H2 close to the Lyβ line using the FUSE satellite

The strongest (Mullikan) band of C2

homonuclear molecule in the HST high res. spectrum

2308 2312 2316

0.90

0.95

1.00

Mullikan band of C2 observed in the HST spectrum of Oph

Rel

ativ

e in

tens

ity

Wavelength

Phillips (2,0) band of C2 molecule in near infrared (BOE and Terskol)

8760 8780 8800

0.98

1.05

1.12

R(0)R(6)

R(4)

R(2)

P(8)P(6)P(2)Q(12)

Q(10)

Q(8)Q(6)

Q(4)Q(2)

ave 15 sp. R=120,000HD24398

HD185859

HD207538

BD+40 4220

HD204827

Rel

ativ

e in

ten

sity

Wavelength

The band of C3 molecule observed with the aid of 3.6m telescope at ESO (spectrograph CES, resolution R=220,000)

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

7694 7696 7698 7700 7702

0.6

0.8

1.0

1.2

1.4

EB-V

=1.26HD 183143

EB-V

=0.26HD 23180 ( Per)

IS KI

Rala

tive

inte

nsi

ty

Wavelength

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

-40 -20 0 20 40

0.3

0.6

0.9

KI

CH

CaI

HD 207198

Rel

ativ

e in

tensi

ty

Radial velocity

Different species may be originated in different clouds; BOE spectrum

-100 -50 0 50 100

0.3

0.6

0.9

CaII

KI

CH

BD +59 2735

Rel

ativ

e in

tensi

ty

Radial velocity

What do the profiles of interstellar features tell us?

Lines of sight toward most of OB stars intercept more than one cloudStrength ratios of Doppler components are different in different featuresRadial velocities measured in different observed features may be differentIt is thus difficult to determine rest wavelengths of features which remain unidentified – like diffuse interstellar bands

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

5720 5760 5800 5840 5880

0.5

1.0

1.5

2.0

58505797

2004/02/12

2004/02/11

2004/02/10

2004/02/09

R

elat

ive

inte

nsity

Wavelength

HD 23180

2004/02/085780

Very broad 6170 DIB, two strong ones and a „forest” of very weak and narrow features;HD210839 (red line), BD +40 4220 (blue line)

6140 6160 6180 6200 6220

0.80

0.88

0.96

1.04

6203

Rel

ativ

e in

tens

ity

Wavelength

6196

Strong and weak diffuse interstellar bands in the spectroscopic binary οPer

5740 5760 5780 58000.90

0.95

1.00

1.05

1.10

2004/10/11

Rel

ativ

e in

tens

ity

Wavelength

2004/10/10

HD 23180

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

-90 -60 -30 0 30 60 90

0.80

0.88

0.96

R

elat

ive

inte

nsity

Radial velocity (km/ s)

CH 4300 A

DIB 6196

(narrowest strong)

DIB 5797

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

5770 5780 5790 5800

0.90

0.95

1.00

Sco EB-V

=0.34

Oph EB-V

=0.3257

80

5797

Rel

ativ

e in

tens

ity

Wavelength

Examples of strength ratios of molecular features and the major DIBs

4230 4260 4290

0.8

0.9

1.0

1.1

1.2

1.3

5780 5790 5800

0.8

0.9

1.0

1.1

1.2

1.3

HD149038

HD154090

Rel

ativ

e in

tens

ity

Wavelength (A)

CH

CH+

CaI HD154368

5780

5797

Narrow DIBs share the Doppler splitting of the CH 4300 line in the spectrum of BD +58 2580

-150 -100 -50 0 50 100

0

1

2

3

4

-150 -100 -50 0 50 100 150

0.90

1.05

1.20

1.35

N

orm

aliz

ed in

tens

ity

Radial velocity

KI 7698 A

CaII 3933 A

CH 4300 A

CH+ 4232 A

CH 4300 A

Rel

ativ

e in

tens

ity

DIB 6196

DIB 6379

DIB 6660

DIB 6993

Details of the 5797 DIB profile observed in ultra high resolution

5796 5797 57980.91

0.98

1.05

Highest spectral resolution in the world

1. UHRF (Siding-Spring Australia) up to R=1,000,000

2. Coude-echelle (KPNO, USA) up to R=500,000

3. Coude-echelle (Terskol, Russia) up to R=520,000

HD 24398 (Terskol)

HD149757 (Siding-Spring)

Inte

nsi

ty

Wavelength (A)

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

Substructures in profiles of weak DIBs – spectra from Gecko

6422 6424 6426 6428 6430

0.99

1.00

1.01

average

HD179406

6436 6438 6440 6442

0.99

1.00

"new" DIB

average

HD 24398

6442 6444 6446 6448

0.98

0.99

1.00

1.01

average

HD179406

Stellar?

6446 6448 6450 6452

0.99

1.00

Rel

ativ

e In

tens

ity

Wavelength (A)

"new" DIB

average

HD 24398

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

-120 -60 0 60 120

0.6

1.2

1.8

2.4

Interstellar lines towards HD184915

5797

6379

KI

CaII

NaIRel

ativ

e in

ten

sity

Radial velocity

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

-50 -25 0 25 50 75

0.0

0.4

0.8

1.2

CH+ 4232A line

Rel

ativ

e in

tens

ity

Radial velocity

NaI D1 line

CaII H lineCH 4300A line

HD 184915

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

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

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

4060 4080 4100 41200.50

0.75

1.00

1.25

Mv = -5.21

Rel

ativ

e in

tens

ity

Wavelength

HD 15785V = 8.34E(B-V)=0.76EW(K)=537mAD(av)=1730pc

HD 24398V = 2.93E(B-V)=0.29EW(K)=57mAD(av)=280pc

Mv = -5.21

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

0 100 200 300 400

-2

0

2

4

6

8

10

EW(KI)

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

0 10 20 30 40 50 60-2

0

2

4

6

8

10

EW(CH)

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

0 20 40 60 80 100 120 1400

2

4

6

8

10

EW(5797)

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

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

-60 -40 -20 0 20 40 60

0.0

0.3

0.6

0.9

Rel

ativ

e in

tens

ity

Radial velocity

HD 210839 - Cep

CH 4300

KI 7699

CaII K 3933

Very tight correlation between column density of H2 and equivalent width of CH 4300 Ǻ line

0 2 4 6 8 10 12 140

10

20

30

40

207198

EW

(CH

) mA

N(H2)1020cm-2

148184

EW(CH)=3.06N(H2)+1.73

r=0.97

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

0 10 20 30 40 50 60 70

0.0

0.5

1.0

1.5

2.0

34078Sco37061

E(B

-V)

EW(CH)

Red-shift of DIBs in the spectrum of HD37061

5780 5790 5800

0.0

0.5

1.0 57975780

HD144217

HD37061R

ela

tive in

tensi

ty

Wavelength

7698.5 7699.0 7699.5

0.0

0.5

1.0 KI

HD37061

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

6192 6194 6196 6198 62000.92

0.94

0.96

0.98

1.00

Rel

ativ

e in

tens

ity

Wavelength

6196

4299.5 4300.0 4300.5 4301.00.60

0.75

0.90

1.05

HD210839

HD 34078

CH

But the abundance of the homonuclear C2 molecule does not correlate with E(B-V)

8750 8760 8770 8780

0.95

1.00

1.05

1.10

E(B-V)=1.05

E(B-V)=1.05

E(B-V)=1.05

E(B-V)=1.39

BD+58 2580

HD219287

HD226868

Rel

ativ

e in

tens

ity

Wavelength

HD204827

BD+59 2735

E(B-V)=1.05

C2 Phillips (2-0) band

As well as that of CN...

3873.0 3874.5 3876.0 3877.5

0.8

1.0

1.2

1.4

HD179406; E(B-V)=0.31

HD 21291; E(B-V)=0.40

HD 34078; E(B-V)=0.50

HD 36371; E(B-V)=0.44

Rel

ativ

e in

tens

ity

Wavelength

HD203064; E(B-V)=0.30

What do correlations between interstellar lines tell us?

The space is filled with clouds dominated with HII, HI and/or H2 depending on physical conditions; many sightlines intercept all kinds of cloudsInterstellar medium is quite evenly filled with HII clouds revealed by the CaII H and K lines, HI and H2 clouds are much smaller geometrically but evidently denser; best correlated carriers should occupy smallest, homogeneous clumpsProper motion of dense clumps may lead to some variability of interstellar features

High S/N profiles of 6614 DIB observed in the same spectra during the same nights; HD144217 is binary

6612 6615

0.96

0.98

1.00

6612 6615

0.96

0.98

1.00

Rel

ativ

e in

tens

ity

McD R=64,0004.05.1993

ESO R=220,00020.06.2000

DIB 6614

HD 144217

Wavelength

HD 149757

DIB 6614

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 H2 clouds contain the carriers of KI, CH, 5797, E(B-V); note that H2 molecules are formed on grainsVast HII clouds of low density and high ionization rate are revealed by the CaII H and K doubletWhere CH+ is located? Hard to say.

Some conclusions...

Strength of CaII lines is quite tightly correlated with distance. They allow to measure distances of OB stars with a reasonable precisionDivision of the observed features into the spectra of HII, HI and H2 clouds allows to describe the spectra of single, homogeneous clouds Measurements of EW(CH) allow to estimate E(B-V) and N(H2) with the precision comparable to the traditional methods