Eta Carinae

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1 FUSE LOCATIONS ON AN IRAS IMAGE(12µ)
2 FUSE LOCATIONS ON AN OPTICAL V IMAGE
3 INTRODUCTION
4 About Eta Carina

[edit] FUSE LOCATIONS ON AN IRAS IMAGE(12µ)

[edit] FUSE LOCATIONS ON AN OPTICAL V IMAGE

[edit] INTRODUCTION

[edit] About Eta Carina

Massive , unstable ,luminous and periodically variable,mass losing star in milky way.Eta carinae is located at the centre of great carina nebula ,a dusty system of massive molecular cloud.High radiation pressure blows significant portion of its outer layer in to space.The distance of carina nebula is 2.7kpc.(M.F Corcoran 2006)

Luminosity of Eta carinae : $4 \times 10^6 L _{\odot}$

Mass : 90 M

Radius : 150 R

Simbad Search result Link:-[ http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=eta+carina&submit=SIMBAD+search]

ICRS coordinates 2000epoc RA = 10 45 03.591 DEC= -59 41 04.26 Galactic coordinates 2000epoc RA = 287.5969 DEC= -00.6295

The star is buried behind the optically thick wall of the homunculus (~10^24cm-2).The twin lobes of the Homunculus are believed to be largely hollow,thin shells (diameter 2.5 pc) separated by a thick disk.Even though interiors of lobes are hollow there is thick condensations within ~200 AU

The observed colors of stars behind the carina nebula will be influenced by

1. Foreground component due to dust between the sun and nebula.

2. Dust which associated with the nebula

3. Dust behind the nebula

Large number of O type stars are found in the Trumpler14, Trumpler16 region of Eta Carina nebula.These are two clusters near to the center of Eta Carina nebula. Therefore reddening law is anomalous.

Total to selective extinction ratio R=Av/E(B-V)=4.8 in Eta Carina nebula. { Either reference or derivation of this value of R is needed. }

It is very high as compared to general interstellar medium in Milky Way. Stars with large range of reddening, are widely distributed within the nebula. E(B-V) color excess for OB stars are anomalously low then the reddening law can be represented by IR color excess. The large value of R implies a grain size distribution larger than normal sized particle and dust composition different to the general interstellar medium {Reference needed.}.

A dark dust lane cuts across the nebula in the vicinity of Tr 14/16 clusters.The absorbing material is in front of Tr 16 cluster and behind the Tr 14 cluster.

(References:Robert G.smith 1986,M.F.Corcoran 2006,Hillier et al (2001),corcoran et al(2001))

The figure shows the approximate distribution of Av derived from the color excess of background field stars. Presence of several heavily reddened early type stars in the southwest corner suggest that the absorbing material is actually in front of Tr16 cluster. The absorbing material continue to northwest and north,it must be behind the Tr14 cluster.A number of our FUSE observed locations are in these regions.

(Reference:Robert G.Smith(1987))

Figure shows a cartoon representation of Eta Carinae system.(Hamaguchi et al 2007)

A sheet of cold material, surrounds the Eta Carinae ,in the walls of homunculus.

[edit] THINGS TO DO

[edit] INTENSITY OF SCATTERED LIGHT

When the electromagnetic wave hits the particle,some light is scattered into the direction specified by the angles $(θ,Φ)$ . Flux of this scattered light by unit volume of dust , $F (θ,Φ)$ which is received at a distance $d 2$ from the dust is proportional to $F_0/d_2^{2}$ .

$dE(\theta,\Phi)= F_0/{d_2^{2}}L(\theta,\Phi) dv$

$L (θ,Φ)$ specifies how the scattered radiation changes with direction.

$f (θ,Φ)$ is the scattering phase function which is proportional to $L (θ,Φ)$

The flux of scattered light we receive on the earth

$dF(\theta,\phi)= F_0/{d_2^{2}} f(\theta,\Phi) \sigma_{sca} dv$

$σ(s c a)$ is the cross section for the scattering of particle. When the light travels through an absorbing medium, it is weakened by extinction.

$d F / d s = - K e x t F 0$

$F = F 0 exp( - τ)$

$dF(\theta,\Phi)= F_0/{{d_2}^{2}} f(\theta,\Phi) \sigma_{sca} \exp(-\tau_1) \exp(-\tau_2) n dv$

$τ 1$ is the optical depth from star to dust and $τ 2$ is the optical depth from the dust to earth.

For spherical volume of cloud we can consider

$dF(\theta)= F_0/{d_2^{2}} f(\theta) \sigma_{sca} \exp(-\tau_1) \exp(-\tau_2) n dv$

This is the measure of energy scattered back to the detector.

From this surface brightness S is given by Energy scattered back to the detector per unit area of cloud per unit solid angle:

$dv=dA\times dz$

$S=F_0/{d_2^{2}} f(\theta) \sigma_{sca} \exp(-\tau_1) \exp(-\tau_2) n \times dA \times dz /d\Omega$

$d Ω = d A / d 22$

$S=F_0 \times f(\theta)\times \sigma_{sca}\times \exp(-\tau_1) \times \exp(-\tau_2) n \times dz$

$τ = n σ d z$

$S=F_0 \times f(\theta)\times \tau \times \exp(-\tau_1) \times \exp(-\tau_2)$

$S=F_0 \times f(\theta)\times \tau \times \exp{-(\tau_1+\tau_2)}$

$S=L/4 \Pi d^{2} \times f(\theta)\times \tau \times \exp{-(\tau_1+\tau_2)}$

$F 0$ be the total energy recieved by the dust per unit time per wavelength through a unit area ( $e r g s / s e c / c m 2 / A 0$ )

energy emitted per sec at a particular wavelength is the luminosity of star.

$F 0 = L / 4Π d 2$

[edit] Optical depth

$τ = n σ d z$

n=number density

$σ$ =dust cross section

dz=elemental distance

$n = (number of hydrogen atom / c m 3)$

n =N(H)/ dz

N(H)=N(H1) + 2N(H)

[edit] Scattering phase function

$f (θ) = a (1 - g 2) / (4Π(1 + g 2 + g c o s (θ)) 1.5)$

$a = a l b e d o$ 0<a<1

$a = σ s c a / σ e x t$

$g = assymmetry factor$ -1 <= g <= 1

$θ$ =scattering angle

$θ = ((x l - x s) x l + (y l - y s) y l + (z l - z s) z l) / dl d$

[edit] Distance

The distance to interstellar dust can be estimated by plotting the reddening vs distance for stars in the direction of Eta Carina nebula. Then we will get an idea about the interstellar dust in Eta Carina nebula and up to what distance it is extending. Then using a triangular method the distance to dust from Eta Carinae can be calculated.

AE the distance of Eta Carina from earth = $(d 1)$

AB= $d 1 c o s (α)$

BE= $d 1 s i n (α)$

$d=\sqrt{d_1^2sin^2(\alpha)+(d_2-d_1cos(\alpha))^2} = \sqrt{d_1^2+d_2^2-2 d_1 d_2 cos(\alpha)}$

Then compare modeled intensity with measured intensity using chi-square minimization, to get optical properties of interstellar dust.

Twin lobs of Eta Carina nebula are believed to be hollow. The UV radiation is scattered by dust in the Interstellar Medium there, but this scattered radiation may get reflected from the cold material in the walls of homunculus.

[edit] PLOTS OF REDDENING VS DISTANCE

Reddening vs distance for stars in Trumpler14/16 cluster ( Ref:Feinstein 1973)

Reddening vs distance for stars in Trumpler15 (Ref:Feinstein 1980)

Reddening vs distance for stars in Collinder 228 (Ref:Feinstein 1976)

Reddening vs distance for stars in Tr14,Tr15,Tr16,Bo 10and Cr228.

From these plots it is clear that dust lies between 2kpc and 4kpc.Eta carinae is at a distance of 2.7kpc,dust sheet in carina nebula lies between 2kpc and 4kpc.Most of our FUSE locations are here.Below 1.5kpc there may be less contribution of dust ,that is clear from the plots.

Why do you say it's clear from the plots? It doesn't look so clear to me. I could even imagine a straight line running through the plots from zero to the maximum E(B-V)

Reddening in eta carinae is anomalous,it is found to be increasing almost upto 1500pc ,that is due to foreground stars,from 2kpc to 4kpc it is almost found that reddening of most of stars between .2 and .6,that means dust may be there.An optically thick sheet of cold materials surrounds eta carinae,that means the scattered light from these dust is not escaping from the nebula ,it may be reflecting back.According to M.F.Corcoran et al (2006),the twin lobs are hollow,but from the plots how we can say that lobs are hollow?,if it is hollow,and surrounding by a thick sheet of dust that reddening of stars in these clusters used to concentrate this dust sheet region only.

[edit] OBSERVATIONS

Intensity of scattered light at 1100Å for four observations in carina nebula is listed in the table above.In these locations total to selective extinction ratio R is 3.1 as predicted by Turner and Moffat (1979).In carina nebula R value is anomalously high in the direction of 14 O type stars R=3.9±.1 (P.S.The,R.Bakker 1980).Two locations are There ,where R value is anomalous ,neutral hydrogen column density in these region is almost same as other locations but molecular hydrogen column density is comparatively high.Distance that given in the table is the distance of each locations from eta carinae.

Two locations are very close to two O type stars HD93205 and HD93204. P.S.The and R.Bakker found that R value in the direction of these two O type stars are anomalous (R=4).R=3.2 ± .28 is applicable to almost whole regions of the carina nebula but R= 3.9 ± .1, in the direction 14 O type stars (P.S.The,R.Bakker 1980). Among these 14 O type stars two are close to these two FUSE observed locations and we can take R=4 in this region.One more possibility also here that scattered radiation in this region may not be due to the radiation from eta carina alone ,radiation from these hot O type stars may also be contributing.

1. One location is found to be at a distance of 6pc from the star.

2. Other one locaion is at a distance of 53pc from the star.

3 R= 3.1 is applicable to this region.Albedo of grains in this region is 0.35 -0.55 corresponding to g =0.4.

4 For other two locations (CPD 592603 ) only R =4 is applicable.But two O type stars in this region.

NEXT STEPS

1. Assume the observed scattered intensity from those two locations (CPD 592603) may be due to the radiation from those two O type stars.

2. Exat distance of these stars from earth.

3. Flux of these stars corresponding to the wavelength 1100A

4. Calculation of Intensity of scattered light from these locations assuming different distance from these O type stars.

5. Albedo and phase function assymetry factor.

HD 93205 is only one O3 star in milkyway known to belong to a double lined binary system.This star is located in the very young open cluster Tr 16.O3V component of HD 93205 is thus potentially a very massive star.This star is about 3100 pc away.FUV flux of this star is higher than that of Eta carinae star.

From this calculations it is seen all these scattering is occurring from dust at a distance 3071pc -3073pc between eta carinae and HD 93205.From this modelling it is seen that scatterring from about five locations are due to the radiation from eta carinae which is at a distance of 3067 pc.Albedo of dust in those regions varying from 0.35-0.55 corresponding to the g value 0.4-0.7 .And scatterring from two locations are due to the radiation from HD 93205 which is at a distance of 3100pc.R value in this direction is 4 and albedo is 0.4-0.5.

[edit] References

1. Hillier, Corcoran et al 2006:- The UV Scattering Halo of the central source associated with $η$ Carinae ApJ, 642,1098-1116

2. Feinstein 1976:- Collinder 228 and $η$ Carinae complex. Astron Astrophysics Suppl, 24, 389.

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