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
HD 149038
Relative intensity
0.9
CH+
0.6
HI
CaII
0.3
"H"
CaII
"K"
3940
3960
Wavelength
3980
„H” line of the same doublet; the orbital period
of oPer is 4.5 days
Spectra of R=120,000 from Terskol echelle spectrometer
Relative intensity
1.0
HD 23180; 25 and 28 Oct. 2001
0.8
0.6
H
3969
3972
Wavelength
3975
Extreme narrowness of the interstellar CaII
line caused by the low density of the medium
(observed at Pic du Midi and Terskol)
Relative intensity
1.0
stellar features
0.8
R=32,000 (Musicos)
0.6
R=120,000 (MAESTRO)
HD 24398
CaII K
3927
3930
Wavelength
3933
Weak and thus rarely observed CaI line in the
spectra of two heavily reddened stars; R=120,000
HD 210839
Relative intensity
1.02
HD 207198
0.96
0.90
CaI
4225
4226
4227
Wavelength
4228
Sodium dublet D1 and D2 discovered by Heger
in 1919 – the lines are usually saturated
Interstellar sodium dublet, Terskol Observatory, R=120,000
HD 24398
Relative intensity
0.8
0.4
0.0
D2
5889
D1
5892
Wavelength
5895
5898
Doublet of neutral potassium; the feature near
7665 A is usually blened with telluric ones. Here
both lines clearly seen in two BOE spectra
HD 23180
Relative intensity
1.2
HD 208501
0.6
Potassium doublet in the spectra of two reddened stars
0.0
7670
7680
Wavelength
7690
7700
Neutral iron lines seen in ultraviolet
Neutral iron interstellar lines in HD 23180
FeI 3859.913 A
1.05
Relative intensity
R=120,000
Terskol Obs.
1.00
0.95
FeI 3719.937 A
-60
-30
0
30
Radial velocity
60
Very weak line of neutral interstellar
Lithium; spectra from BOE spectrograph
1.04
Relative intensity
BD +60 594
1.02
BD +40 4220
1.00
HD204827
0.98
6706
LiI
6708
Wavelength
6710
The extremely weak line of neutral
interstellar rubidium
RbI interstellar line in averaged spectra from two spectrographs
Relative intensity
1.008
MAESTRO spectrograph, R=120,000
1.000
BOE spectrograph, R=30,000
0.992
RbI
7796
7800
Wavelength
7804
Oxygen, sulphur and phosphorus in HST
spectra taken with high resolution
Relative intensity
Oxygen dublet in far-UV HST spectrum of XPer
PII
0.8
SI
0.4
PII
0.0
OI
OI
1302
1303
Wavelength
1304
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
1.0
HD 210839
H lab.
Relative intensity
HD 207198
0.9
0.8
0.7
4855
4860
Wavelength
4865
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 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;
2004/02/09
Relative intensity
1.08
0.99
2004/02/12
0.90
HD 23180
4280
CH
4300
Wavelength
4320
Very narrow profile of the polar CH radical observed
at CFHT (R=32,000) and at Terskol (R=120,000)
Relative intensity
CH
0.96
PdM R=32,000
Terskol R=120,000
0.88
 Per
0.80
4299.6
4300.0
4300.4
Wavelength
4300.8
4301.2
Variable physical conditions in interstellar
clouds: neighbour features of CaI and CH+;
(spectra from Terskol, R=120,000)
Relative intensity
1.1
HD207198
1.0
CaI
HD24912
0.9
+
0.8
CH
4227
4230
Wavelength
4233
Sequence of interstellar molecular features;
note the variable CN/CH strength ratio
HD 34078
HD 179406
CH
CH
CH
CN
1.0
CN
0.8
CN
Relative intensity
1.2
3876
3882
Wavelength
3888
Different rotational CN temperatures
towards two reddened stars; Gecko high res.
Relative intensity
HD 206165
1.0
HD 208501
0.8
0.6
Gecko/CFHT
3873
3874
3875
Wavelength
3876
3877
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
Relative intensity
Mullikan band of C2 observed in the HST spectrum of Oph
1.00
0.95
0.90
2308
2312
Wavelength
2316
Phillips (2,0) band of C2 molecule
in near infrared (BOE and Terskol)
HD24398
ave 15 sp. R=120,000
Relative intensity
1.12
HD185859
HD207538
1.05
BD+40 4220
0.98
Q(10)P(6)
P(2)
R(6)
R(4)
R(2)
Q(6)
R(0)
Q(12)P(8)
HD204827
Q(8)
Q(4)
Q(2)
8760
8780
Wavelength
8800
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 Dopplersplitted; the medium is not homogeneous
Ralat ive int ensit y
1.4
HD 23180 ( Per)
EB-V=0.26
HD 183143
EB-V=1.26
1.2
1.0
0.8
0.6
IS KI
7694
7696
7698
7700
Wavelengt h
7702
Radial velocities of different species are not
identical; here the R=120,000 Terskol spectrum
HD 207198
CaI
Relative intensity
0.9
CH
KI
0.6
0.3
-40
-20
0
Radial velocity
20
40
Different species may be originated in
different clouds; BOE spectrum
BD +59 2735
Relative intensity
0.9
CH
KI
0.6
CaII
0.3
-100
-50
0
Radial velocity
50
100
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
Doppler dance of stellar lines in the spectroscopic
binary oPer; sodium doublet and diffuse bands are
stationary (spectra from BOES)
2004/02/12
2.0
Relative intensity
2004/02/11
2004/02/10
1.5
2004/02/09
1.0
2004/02/08
5780 5797
5850
0.5
HD 23180
5720
5760
5800
Wavelength
5840
5880
Very broad 6170 DIB, two strong ones and a „forest”
of very weak and narrow features;
HD210839 (red line), BD +40 4220 (blue line)
Relative intensity
1.04
0.96
0.88
6203
6196
0.80
6140
6160
6180
Wavelength
6200
6220
Strong and weak diffuse interstellar bands in
the spectroscopic binary οPer
2004/10/10
1.10
Relative intensity
1.05
2004/10/11
1.00
0.95
HD 23180
0.90
5740
5760
5780
Wavelength
5800
High resolution (R=120,000) profiles of two narrow
DIBs compared to that of CH feature in ζPer
Relative intensity
0.96
CH 4300 A
DIB 6196
0.88
(narrowest strong)
DIB 5797
0.80
-90
-60
-30
0
30
Radial velocity (km/s)
60
90
Variable strength ratio of the major
DIBs; spectra R=32,000 from CFHT
5797
Relative intensity
1.00
0.95
 Oph EB-V=0.32
 Sco EB-V=0.34
5780
0.90
5770
5780
5790
Wavelength
5800
Examples of strength ratios of molecular
features and the major DIBs
1.3
1.3
HD149038
Relative intensity
1.2
1.2
HD154090
1.1
1.1
1.0
1.0
CaI
0.9
HD154368
CH+
0.9
5780
5797
0.8
0.8
CH
4230
4260
4290
Wavelength (A)
5780
5790
5800
Narrow DIBs share the Doppler splitting of the CH
4300 line in the spectrum of BD +58 2580
4
3
DIB 6660
CH 4300 A
2
CaII 3933 A
Relative intensity
Normalized intensity
DIB 6993
1.35
CH+ 4232 A
1.20
DIB 6379
DIB 6196
1.05
1
KI 7698 A
CH 4300 A
0.90
0
-150 -100 -50
0
50
100
-150 -100 -50
Radial velocity
0
50 100 150
Details of the 5797 DIB profile
observed in ultra high resolution
HD149757 (Siding-Spring)
Highest spectral resolution
in the world
1.05
Intensity
1. UHRF (Siding-Spring Australia)
up to R=1,000,000
2. Coude-echelle (KPNO, USA)
up to R=500,000
HD 24398 (Terskol)
0.98
3. Coude-echelle (Terskol, Russia)
up to R=520,000
0.91
5796
5797
Wavelength (A)
5798
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
HD179406
HD 24398
1.01
1.00
average
average
1.00
"new" DIB
0.99
Relative Intensity
0.99
6422
6424
6426
6428
6430
6436
6438
6440
6442
HD 24398
HD179406
1.01
1.00
1.00 average
average
0.99
Stellar?
"new" DIB
0.99
0.98
6442
6444
6446
6448
6446
Wavelength (A)
6448
6450
6452
Interstellar features may be formed in
different clouds along the same sight-line
Interstellar lines towards HD184915
5797
6379
Relative intensity
2.4
KI
1.8
CaII
1.2
NaI
0.6
-120
-60
0
Radial velocity
60
120
Narrow IS features in the same object as
above but R=120,000 (Terskol)
1.2
+
CH 4232A line
CH 4300A line
Relative intensity
CaII H line
NaI D line
1
0.8
0.4
HD 184915
0.0
-50
-25
0
25
Radial velocity
50
75
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
1.25
Relative intensity
HD 15785
V = 8.34
E(B-V)=0.76
EW(K)=537mA
D(av)=1730pc
1.00
Mv = -5.21
HD 24398
V = 2.93
E(B-V)=0.29
EW(K)=57mA
D(av)=280pc
Mv = -5.21
0.75
0.50
4060
4080
4100
Wavelength
4120
Neutral potassium does not correlate with
distance. The same sample as in the former slide.
10
8
6

4
2
0
-2
0
100
200
EW(KI)
300
400
The absorption feature of CH (4300 A) does not
correlate with trigonometric parallax
10
8
6

4
2
0
-2
0
10
20
30
EW(CH)
40
50
60
The major 5797 diffuse band does not
correlate with the trigonometric parallax
10
8

6
4
2
0
0
20
40
60
80
EW(5797)
100
120
140
The lack of correlation between E(B-V) and
distance
Different radial velocities and profiles
of various interstellar lines (R=120,000)
Relative intensity
0.9
CH 4300
0.6
KI 7699
0.3
0.0
CaII K 3933
HD 210839 - Cep
-60
-40
-20
0
Radial velocity
20
40
60
Very tight correlation between column density of
H2 and equivalent width of CH 4300 Ǻ line
EW(CH)=3.06N(H2)+1.73
EW(CH) mA
40
r=0.97
30
207198
148184
20
10
0
0
2
4
6
8
20
N(H2)10 cm
10
-2
12
14
E(B-V) colour excess is very well correlated
with the line strength of CH radical
2.0
E(B-V)
1.5
1.0
0.5
37061
Sco
34078
0.0
0
10
20
30
40
EW(CH)
50
60
70
Red-shift of DIBs in the spectrum
of HD37061
HD37061
HD37061
KI
1.0
Relative intensity
HD144217
0.5
0.0
7698.5
1.0
7699.0
7699.5
5797
5780
0.5
0.0
5780
5790
Wavelength
5800
Blue-shift of diffuse band in the
spectrum of AE Aur (HD34078)
1.05
CH
0.90
HD210839
HD 34078
Relative intensity
0.75
0.60
4299.5
4300.0
4300.5
4301.0
6196
1.00
0.98
0.96
0.94
0.92
6192
6194
6196
Wavelength
6198
6200
But the abundance of the homonuclear C2
molecule does not correlate with E(B-V)
E(B-V)=1.05
Relative intensity
BD+58 2580
1.10 HD219287
E(B-V)=1.05
HD226868
E(B-V)=1.05
BD+59 2735
E(B-V)=1.39
HD204827
E(B-V)=1.05
1.05
1.00
0.95
C2 Phillips (2-0) band
8750
8760
8770
Wavelength
8780
As well as that of CN...
HD203064; E(B-V)=0.30
1.4
HD 36371; E(B-V)=0.44
Relative intensity
HD 34078; E(B-V)=0.50
1.2
HD 21291; E(B-V)=0.40
HD179406; E(B-V)=0.31
1.0
0.8
3873.0
3874.5
3876.0
Wavelength
3877.5
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 clouds
Interstellar 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 clumps
Proper 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
Relative intensity
DIB 6614
DIB 6614
1.00
1.00
ESO R=220,000
20.06.2000
0.98
0.98
McD R=64,000
4.05.1993
0.96
HD 149757
HD 144217
6612
6615
6612
Wavelength
6615
0.96
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 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.
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 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