and their native cluster - university of...

Constraining massive star evolution

and their native cluster

André-Nicolas Chené – Gemini Observatory F. Martins (U.Montpellier), A. Hervé (AICAS), J.-C. Bouret (LAM),

J. Borissova (U. Valparaiso), the VVV science team

!   This presentation covers a fraction of the work done by

the star Cluster Group in the VVV survey Science

team.

!   VVV is for “VISTA Variable in Via Lactea”. It is one of

the 6 ESO public surveys based at the VISTA telescope

at Paranal, Chile. On the next slide, you can see basic

parameters of the survey. It covers the bulge area of the

Milky Way (MW) and an adjacent part of the inner

disk.

VISTA Variables in the Via Lactea

!   ~2000 hours on the VISTA (ESO, Paranal) telescope

!   ZYJHKS

!   ~109 sources

!   562 deg2

(Minniti et al. 2010,

Saito et al. 2012,

Hempel et al. 2014)

!   The original driving science questions motivating the

work of our group are presented in the following slide.

Driving science questions

!   Where are the missing clusters in the MW (10x) ?

!   Are there R136s in the MW ?

!   What can we find when we compare a wide

variety of cluster parameters?

!   Since VVV is in infrared, we can observe highly

obscured sources. Compared with the 2MASS survey

(performed in similar wavelength bands), VVV

observed a selected part of the MW, but goes much

deeper.

!   M dwarfs up to ~6 kpc

!   G dwarfs up to ~8 kpc

!   RR Lyrae up to > 35 kpc

!   Giant clump stars across the MW

VVV coverage

2 MASS vs VVV

limits

2 MASS

VVV

M-dwarf G2 dwarf RR Lyrae Clump giants

!   This is a mosaic of the MW’s bulge. It follows with a

series of zoomed images towards the Galactic Center.

!   You can navigate through this image at:

!   https://www.eso.org/public/unitedkingdom/images/

eso1242a/zoomable/

VVV bulge area (zoomable)

VVV bulge area (zoomable)

VVV bulge area (zoomable)

VVV bulge area (zoomable)

VVV bulge area (zoomable)

VVV bulge area (zoomable)

VVV bulge area (zoomable)

VVV bulge area (zoomable)

VVV bulge area (zoomable)

!   The next slide compares the spatial resolution and the

depth achieved with VVV and 2MASS.

!   VVV photometry reaches a 0.5 mag accuracy down to

KS=20 mag (about 0.1 mag down to KS=18 mag).

!   VVV saturates at KS<12 mag.

!   2MASS photometry reaches 0.5 mag down to KS=15

mag.

!   2MASS suffers from crowding in the clustered areas.

VVV – deep, high resolution

VVV 2MASS

!   VVV survey matches other surveys in sub-mm, MIR,

Optical, allowing multi-wavelength studies.

!   All REDUCED data and aperture photometry catalogs

are available here:

! http://archive.eso.org/wdb/wdb/adp/phase3_main/form?

phase3_program=VVV&phase3_collection=VVV&release_tag=1

!   Images are *_st_tl.fits.fz. Phometry catalogs are

_st_tl_cat.fits

!   Consult these papers for more details: ! https://www.eso.org/sci/observing/phase3/data_releases/vvv_dr4.pdf

! https://www.eso.org/sci/observing/phase3/data_releases/VVV_DR2_CAT.pdf

VVV matches other surveys

APEX

GLIMPSE

VVV

Optical

!   VVV achieved not only JHKS imaging, but also KS

repeated observations over the last 6 years, opening the

time domain!

!   This is an example of the recent discovery of a nova or

supernova toward the central area of the Galaxy!

!   Other time domain studies are variable stars, binaries,

lensing effects and proper motions.

VVV-WIT-05: An Extreme

Transient of Unknown

Nature in the VVV Survey

!   Possible new supernova discovered in the Milky Way!

(peaked in Aug 2011 - ATel #8869)

!   The search and study of open clusters is part of the

original proposal for the VVV large survey.

Original VVV science goals

1. To find RR Lyrae in the bulge

2. To identify variable stars belonging to known star clusters.

3. To find eclipsing binaries in large numbers.

4. To find rare variable sources.

5. To search for microlensing event.

6. To monitor variability around the Galactic center.

7. To search for new star clusters of different ages. 8. To provide complementary near-IR multi-colour information.

9. To find variable stars in the Sgr dSph galaxy.

10. To identify high-proper motion objects and background QSOs.

11. To identify pre-MS clusters and associations through variability.

!   The details of the newly 735 discovered bona fide

clusters are published in:

! Borissova et al. (2011, 2014)

! Solin et al. (2014)

! Barba et al. (2015)

735 bona fide clusters

discovered in VVV

!   The discovery of many young open clusters opens the

opportunity for more case studies to constrain massive

star evolution.

!   The following description of the evolution path is

pretty uncertain and inaccurate. But it is close to the

best we have for now. Note that the place of the LBV

phase here is strongly debated (as shown by Jeremiah

Murphy’s presentation of Nathan Smith’s work at this

conference).

New potential clusters to study

stellar evolution! !   Current scenario not known in detail…

! Binarity?

! Metallicity?

!   Rotation?

!   Enrichment?

O

SG

LBV

WR

25 - 40 M¤

40 - 75 M¤

> 75 M¤ WNha

WN ( WC)

SN

?

time (not to scale)

Crowther (2007, ARA&A, 45, 177)

!   Here I offer you a nice analogy that we use often in

stellar evolution:

!   Studying young cluster is like studying a kindergarten

class room:

!   They were born more or less at the same time,

!   The evolution depends on the metallicity enrichment of

the environment,

!   Off course, some might have evolved in multiple

systems.

!   Don’t mind the astronomer in the background…

Young open clusters are great

to study stellar evolution

Stellar evolution

!   Older clusters are a mess:

!   Ages are very different. Some are very evolved while

others are recently formed

!   The most influential ones are long gone…

!   Off course, there are limits to any analogy (details of

star formation).

Older clusters

are not as good…

Stellar evolution

!   Arches cluster is young, massive, has main sequence

and evolved stars togther…

!   The detail study of its HR diagram confirms the

Crowther et al. (1995) scenario of the evolution of O

stars to WNLh stars.

Arches is perfect!

6

5.5

4.7 4.5 4.3

Lo

g (L

/L¤

)

Log (T*) Martins et al. (2013)

!   Confirms the Crowther

et al. (1995) scenario: !   O → Of → WNL+abs → WN7

!   Age is 2-4 Myrs, but

WNLh seem 2-3 Myr old

Stellar evolution

!   Here are the clusters that were discussed in detail so far in this conference (+ some others).

!   The inner colour represents the age (the redder the older), and the colour of the annulus around each point represents Av (the redder the more extinct).

!   The clusters are:

! Westerlund 1

!   NGC 3603 (Crowther et al. 2010)

!   Quartet (Martins et al. 2008)

!   Quintuplet (Liermann et al. 2012)

!   Arches (Martins et al. 2008)

!   Mercer 81

Well studied

young clusters 10

-5

0 0

5

-5

Y (

kp

c)

X (kpc)

l (deg)

b (

deg

)

10

-15 -60 0 20

! Westerlund 1

!   NGC 3603 (Crowther et al. 2010)

!   Quartet (Martins et al. 2008)

!   Quintuplet (Liermann et al. 2012)

!   Arches (Martins et al. 2008)

!   Mercer 81 (Davies et al. 2012)

!   Now, we are adding 9 new VVV clusters with OB and

evolved (i.e. WR, RGS, BSG) stars.

9 new young

clusters in VVV !   < 10Myrs

!   w/ OB stars

!   w/ Evolved stars

(RSG, BSG, WR)

!   ~ 1000 M¤

total

10

-5

0 0

5

-5

Y (

kp

c)

X (kpc)

l (deg)

b (

deg

)

10

-15 -60 0 20

!   Here are 7 of the new VVV clusters with WR stars.

7 clusters with WR stars 10

14

18

KS

1 6 J-KS

0 5 J-KS

3 8 J-KS

3 8 J-KS

8

12

18

1 5

KS

J-KS

10

14

18

3 8

KS

J-KS

009 011 036 073

2 7 J-KS

074 099 041

Chené et al. (2013, 2015)

!   Preliminary results for VVV CL074, which has many

Of stars, some WN stars and one WC star.

!   Spectra of fainter targets are expected later this year! We

aim to go down to KS=14 mag to reach the pre-main

sequence turn-off.

~40 M¤

with WN8 in VVV CL074

10

14

18

3 8

KS

J-KS

(spectra of fainter targets coming soon)

Log (T*) 4.7 4.4

6.0

5.0

Lo

g (L

/L¤

) 1Myr

3Myr

5Myr

VVV CL074

7Myr

WC8

WN8

O4-6If

O8.5I

Hervé et al. (2016)

!   Interesting finding of a Very Massive Star (WR62-2) in

a ~1000 M¤

cluster.

8

12

18

1 5

KS

J-KS

α (212.00°) 64 57

37

40

δ (−

59.0

0°)

New VMS (WR62-2) in VVV CL041

(Monitoring of the

most massive stars

coming soon)

4.7 4.4

25M¤

40M¤

80M¤

60M¤

120M¤

Log (T*)

VVV CL041

WN8ha

O stars

6.0

5.0

Lo

g (L

/L¤

)

WR62-2

Chené et al. (2015)

!   VVV will cover hundreds of well studied NEW clusters.

Here are the 50 we have completed so far.

! Borissova, J., Chené, A.-N., Ramirez Alegria, S. et al. 2014,

! Chené, A.-N., Borissova, J., Bonatto, C., et al. 2013, A&A,

549, A98

! Chené, A.-N., Borissova, J., Clarke, J. R. A., et al. 2012, A&A,

545, A54

! Chené, A.-N., Ramirez Alegria, S., Borissova, J., et al. 2015,

A&A, 584, A31

! Corti, M. A., Baume, G. L., Panei, J. A. et al. 2016, accepted

in A&A (arXiv:160102718C)

! Ramirez Alegria, S., Borissova, J., Chené, A.-N., et al. 2014,

! Ramirez Alegria, S., Borissova, J., Chené, A.-N., et al. 2016,

A&A, 588A, 40

Homogeneous

database 10

-5

0 0

5

-5

Y (

kp

c)

X (kpc)

l (deg)

b (

deg

)

10

-15 -60 0 20

Compare clusters with

different:

!   Age

! Metallicity

!   Mass

!   etc.

!   Here we present a summary of preliminary results

when comparing different cluster parameters.

!   We limit this preliminary study to young clusters.

!   The covered parameters are:

!   AV

!   Age

!   Total mass

!   Mass of the most massive star

!   Number of WR stars

!   Radius

!   The following shows a correlation between the number

of WR stars and AV.

!   But this correlation is dominated by Arches,

Quintuplet and the GC cluster that contain more than

half of the known Galactic WR in clusters.

Number of WR stars correlates

with the Extinction (AV)

Arches, Quintuplet and

Galactic Center clusters ?

Kendall's τ rank

correlation coefficient

!   The following shows a correlation between the number

of WR stars and the mass of the most massive star.

!   But this correlation can come from small number

statistic, due to the small number of clusters with WR

stars that we know.

Number of WR stars correlates

with the Mass of the most massive star

Small number statistic ?

Kendall's τ rank

correlation coefficient

!   The following shows a correlation between the number

of WR stars and the cluster total mass.

!   But this correlation can come from a selection effect, as

we can more easily discover the most massive clusters.

The Total Mass of the cluster correlates

with the number of WR stars

Selection effect ?

Kendall's τ rank

correlation coefficient

!   The following shows a correlation between the mass of

the most massive star and the cluster total mass.

!   This corresponds to the relation presented in Weidner

et al. (2010). This is interesting, since the Weidner et al.

study should be plagued with many statistical issues.

We need to check if this survives the addition of the

future datapoints.

!   We might have an outlier (VVV CL041)?

The Total cluster Mass correlates

with the Mass of the most massive star

Weidner et al. (2010) ?

Kendall's τ rank

correlation coefficient

The Total cluster Mass correlates

with the Mass of the most massive star

Weidner et al. (2010) ?

Kendall's τ rank

correlation coefficient

VVV CL041

!   The following shows a correlation between the age and

the mass of the most massive star

!   There seem to be a turn-off point at 4Myrs? Could it be

from stellar evolution?

!   Too good to be true? I don’t know, but too few points,

certainly.

The Age anti-correlates

with the Mass of the most massive star

Stellar evolution ?

Kendall's τ rank

correlation coefficient

The Age anti-correlates

with the Mass of the most massive star

Stellar evolution ?

Kendall's τ rank

correlation coefficient

4Myrs

!   The following shows a correlation between the age and

the total cluster mass

!   There seem to be a turn-off point at 3Myrs? Could it be

from cluster evolution?

!   Again, too good to be true?

The Age anti-correlates

with the Total cluster Mass

Cluster evolution ?

Kendall's τ rank

correlation coefficient

The Age anti-correlates

with the Total cluster Mass

Cluster evolution ?

Kendall's τ rank

correlation coefficient

3Myrs

!   All these preliminary results are to take with a grain of

salt. I expect that in 3 more years, in a conference

maybe entitled “From Stars to Star Clusters”, I will

present you stronger results covering a much wider

cluster parameter space. Current proposals are in the

hands of time allocation comities to decide if we get

the programs that will allow us to push much further,

reaching more remote/obscured clusters and/or less

massive clusters.

!   I leave you with this short summary and conclusion.

Summary and conclusion

!   Phases of the project:

!   First pass (photometry + spectroscopy)

!   More accurate (more spectra – LLP)

!   Proper motion (from VVV KS series)

!   Detail individual (dedicated programs on selected clusters)

!   Current results:

!   PSF photometry of ~1500 clusters (candidates)

!   First study of 50 new (confirmed) clusters

!   Discovery of > 12 WR stars

!   Discovery of a remote young cluster