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