Eta Carinae

Zulema Abraham IAG/USP

Introduction

Star itself

Ejecta, Great Eruption in 1840 formed the Homunculus

The 5.52 yr periodicity

Binary vs shell

Homúnculo

Carinae

Homúnculo

Carinae

D = 2.3 kpc

The Star

Frew, JAD 10, 6 (2004)Great Eruption

(1837)

Lesser Eruption(1887-1895)

Homunculus ?

Frew, JAD 10, 6 (2004)Great Eruption

(1837)

Lesser Eruption(1887-1895)

Frew, JAD 10, 6 (2004)Great Eruption

(1837)

Lesser Eruption(1887-1895)

Homunculus ?

Carinae: The Star

Luminous Blue Variable

If single M > 120 M

Mass loss rate: 10-4 – 10-5 M /yr Spectrum: broad and narrow

permitted and forbidden emission lines.

No photospheric lines are visible

Some lines present P Cygni profiles

Humphreys-Davidsonlimit

(Humphreys & Davidson 1994, PASP 106, 1025)

The ejecta

Ejecta: Homunculus in Expansion

Morse et al. 2001, ApJ, 548, L207

1890

1846

Hubble like expansion law, Curie et al. 1996, AJ, 112, 1115

The Homunculus at the IR

Ejected mass was calculated from the visual extinction and line emission as 2.5 M (Davidson & Humphreys 1997)

Mid to far-IR ISO observations showed a spectrum compatible with three T dust emission from 15 M (Morris et al. 1999).

Smith et al. (2003) came to the same conclusion from 4.8-24.5 m images obtained with the 6.5 m telescope from the Magellan observatory

LBV or supernova?

Morris et al. 1999, Nature, 402, 502(dust torus in the equator)

Smith et al. 2003, AJ, 125, 1458(dust at the poles)

The Little Homunculus

Ishibasbhi et al. (2003) dicovered the LH using the long-slit Space Telescope Imaging Spectrograph

Smith (2005) presented Doppler tomography of the [Fe II] 16435 line obtained with the Gemini South telescope

[FeII] 16435

Smith 2005, MNRAS, 357,1330

Ishibashi et al. 2003, AJ, 125, 3222

Homunculus in X-rays

Weis et al. 2004, A&A, 415, 595

0.6-1.2 keV

1.2 -11 keV

0.2 – 11 keV

The 5.52 yr periodicity

Periodicity in the high-excitation lines

Damineli (1996) found a 5.52 years periodicity in the He I 10830 line intensity

It is anticorrelated with the H-band infrared emission.

Damineli 1996, ApJ, 460, L49Whitelock et al. 1994, MNRAS, 270,364

Periodicity in the IR

Periodicity at optical wavelengths

Fernandez Lajus et al. 2003, IBVS, 5477

Periodicity at X-rays (RXTE)

Corcoran 2005,AJ, 129, 2018

Dec 1997

Jun 2003

Radio Images with ATCA

Observed at 3 and 6 cm with ATCA since 1992 (Duncan et al. 1995,1996)

Different structures show different velocities

Slow velocity region has an edge-on disk-like structure

edge on disk (Duncan & White 2003)

Radio Observations at SEST and Itapetinga

Observed with SEST at 1.3, 2 and 3 mm

Flux density increases with frequency

Variable light curve, in phase with optical emission

At Itapetinga, scans across the source, calibrated with G287.57-0.59

Car Car

Cox et al. 2005, A&A, 297,168

Retalack, 1983 (1415 MHz)

Car Car

Cox et al. 2005, A&A, 297,168

Retalack, 1983 (1415 MHz)

0

5

10

15

20

25

30

35

40

45

1990 1992 1994 1996 1998 2000 2002 2004

Epoch (years)

Flux

Den

sity

(jy)

0

200

400

600

800

1000

1200

1 mm

HeI

0

5

10

15

20

25

30

35

40

45

1990 1992 1994 1996 1998 2000 2002 2004

Epoch (years)

Flux

Den

sity

(jy)

0

200

400

600

800

1000

1200

1 mm

2 mm

HeI

0

5

10

15

20

25

30

35

40

45

1990 1992 1994 1996 1998 2000 2002 2004

Epoch (years)

Flux

Den

sity

(jy)

0

200

400

600

800

1000

12001 mm

2 mm

3 mm

HeI

0

5

10

15

20

25

30

35

40

45

1990 1992 1994 1996 1998 2000 2002 2004

Epoch (years)

Flux

Den

sity

(jy)

0

200

400

600

800

1000

12001 mm

2 mm

3 mm

7 mm

HeI

0

5

10

15

20

25

30

35

40

45

1990 1992 1994 1996 1998 2000 2002 2004

Epoch (years)

Flux

Den

sity

(jy)

0

200

400

600

800

1000

12001 mm2 mm3 mm7 mm3.5 cmHeI

Periodicity at mm wavelengths

Last Event (2003.5)

Abraham et al. 2005, A&A, 437, 997

SEST

Itapetinga

SEST

Itapetinga

Last minimum: 7 mm and X-rays

Radio vs X-rays

-505

10152025303540455055

2003.0 2003.5 2004.0 2004.5 2005.0

date (years)

X-ra

ys fl

ux ..

.

0

1

2

3

4

5

6

7

8

7 m

m fl

ux d

ensi

ty (

Jy) .

......

x-raysradio

What do the coincidence tell us?

7 mm flux density is due to the free-free emission from an optically thick disk (density about 107 cm-3)

Sharp minimum is produced by a decrease in the number of available ionizing photons (recombination time of the order of hours)

Decrease in the number of photons is due to absorption of UV radiation by dust

The same material that absorbs the UV absorbs X-rays

Binary vs shell

Shell events Zanella, Wolf & Stahl 1984, A&A, 137, 79

A binary system?

The 5.52 yr periodicity was also found in the radial velocity of the broad component of the Pa lines.

It was compatible with a binary system with eccentricity e = 0.6

Minimum in the He I line curve occurs at periastron passage

Predicted strong wind-wind interactions

Damineli et al. 1997, New Astr., 2, 107

Orbital Parameters: eccentricity

The orbital parameters were not very well determined

Davidson (1997) use the same data and gave different parameters, specially higher eccentricity

Davidson 1997, New Astron.,

Davidson (1997)

Data and orbit f romDamineli et al. (1997)e = 0.63

Data f romDamineli et al. (1997), diff erentepoch for periastronand e = 0.67

Data f romDamineli et al. (1997), diff erentepoch for periastronand e = 0.80

Davidson (1997)

Data and orbit f romDamineli et al. (1997)e = 0.63

Data f romDamineli et al. (1997), diff erentepoch for periastronand e = 0.67

Data f romDamineli et al. (1997), diff erentepoch for periastronand e = 0.80

X-rays: wind-wind collisions

Pittard 2003, A&G, 44, 17

Numerical simulations

Pittard & Corcoran 2002, A&A, 383, 636

T 108 K

Density profile (g cm-3)

1.0pp

ss

MM

4103 pM510sM

M /yr 500p

1500skm/sDensity profile

(g cm-3)1.0

pp

ss

MM

4103 pM510sM

M /yr4103 pM

510sMM /yr 500p

1500skm/s

500p

1500skm/s

Position of periastron (near opposition)

Position of periastron (near opposition)

Mass in the line of sight necessary toproduce the observed absorption

Dust formation near periastron

Two shocks form at both sides of the conical contact surface

Near periastron the density of the shocks is very high and the region cools radiatively

After the secondary star moves in the orbit, a cold region can be formed between the two shocks and dust can grow.

The accumulated dust absorbs X-rays and optical emission

Falceta-Gonçalves, Jatenco-Pereira & Abraham 2005,MNRAS, 357,895

Position of periastron (near conjunction)

125

410 pM M /ano

125

410 pM M /ano

e = 0.9

e = 0.95

e = 0.9

e = 0.95

Determination of the orbital parameters from the 2003.5 event

Decrease in the radio flux is due to the decrease in the number of ionizing photons

Peak seen at 7 mm was due to free-free emission from the shock (T107 K, ne1011 cm-3)

Peak at 1.3 mm is not seen because of lack of resolution.

Abraham et al. 2005, A&A, 437, 997

SEST

Itapetinga

SEST

Itapetinga

Determination of the orbital parameters from the 2003.5 event

Shock material is optically thick at 7 mm and optically thin at 1.3 mm

The material of the secondary shock produces most of the flux density

The observed light curve at 7 mm is explained by geometrical factors.

Abraham et al. 2005, A&A, 437, 997

SEST

Itapetinga

SEST

Itapetinga

Fitting the 7 mm light curve

Abraham et al. 2005, MNRAS….

Orbital Parameters

-10

0

10

20

-20 0 20 40 60

time (days)

1.3

mm

flux

den

sity

(Jy)

------

)

0

1

2

3

4

7 m

m fl

ux d

ensi

ty (J

y)---

----

7 mm

1.3 mm

0

5

10

15

20

-20 0 20 40 60

time (days)

1.3

mm

flux

den

sity

(Jy)

-----

-

0

5

10

15

20

Conclusions (personal)

Star: LBV or supernova? Still unknown

Binary system or shell event: both

Orbital parameters: only determined from radio at periastron passage: they imply that periastron is close to conjunction.