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