Hubble Science Briefing: 25 Years of Seeing Stars with the Hubble Space Telescope
March 5, 2015
Dr. Rachel Osten
Dr. Alex Fullerton
Dr. Jay Anderson
Hubble’s Insight into the Lives of Stars Comes From:
Better image clarity: no atmosphere, no blurring means higher spatial resolution
Access to ultraviolet wavelengths: not possible from the ground
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Outline
• Rachel Osten - cool stars • Alex Fullerton - massive stars • Jay Anderson – globular clusters
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The UV spectrum of a Sun-like star
Hot gas (>10,000 K) means that many elements are ionized Hotter than the visible surface of the star (Sun=5800 K)
Linsky & Wood 1994 5
The UV spectrum of a Sun-like star
Pagano et al. 2004
Brightness
Alpha Cen A at higher spectral resolution than UV spectra from the Sun!
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The UV spectrum of a Sun-like star
Linsky & Wood 1994
Brightness
Dynamics of the atmosphere
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The UV spectrum of a Sun-like star
Brightness Time (seconds)
The changing of a star’s intensity with time on these short timescales is due to heating from flares occurring in the atmosphere of the star
Hawley et al. (2003)
0 200 400 600 800 0 200 400 600 800
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Stars Blow Bubbles in Space
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Stars Blow Bubbles in Space
Wood et al. 1995 10
Stars Blow Bubbles in Space
Wood et al. 2002
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Stars Blow Bubbles in Space
Linsky et al. 2010
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Outline
• Rachel Osten - cool stars • Alex Fullerton - massive stars • Jay Anderson – globular clusters
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Massive Stars
Image Source: kids.britannica.com
1 Solar Mass 1 Solar Radius 1 Solar Luminosity T = 5,800 Kelvin
4 - 300 (?) Solar Masses 3,000,000 Solar Luminosities Temperature: 10,000 – 50,000 Kelvin Radius: 2 – 15 Solar Radii 30 Solar Radii T = 7,500 – 3, 600 Kelvin R = 80 – 8, 000 Solar Radii
Massive stars can be luminous because they are • hot and compact • hot and large • cool and very large
Massive stars are also luminous stars.
“Red” supergiants
The Kelvin Temperature Scale: K =5
9F -32( ) + 273.15
“Blue” supergiants
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R136
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Space Telescope Imaging Spectrograph (STIS) From a poster paper by A. Bostroem, N. Walborn, et al.
“P Cygni Profiles” tell us about mass loss via a “stellar wind”
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The Carinae Region: A Cauldron of Hot, Massive Stars
This spectacular montage was created to celebrate the 17th anniversary of Hubble’s deployment. It is composed of many separate exposures with Hubble’s Advanced Camera for Surveys (ACS) and ground-based images from the Cerro Tololo Inter-American Observatory (CTIO). For a fuller appreciation of its information content, explore the “zoomable” version: http://hubblesite.org/newscenter/archive/releases/2007/16/image/a/format/zoom/
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The Carinae Region: A Cauldron of Hot, Massive Stars
η Carinae
This spectacular montage was created to celebrate the 17th anniversary of Hubble’s deployment. It is composed of many separate exposures with Hubble’s Advanced Camera for Surveys (ACS) and ground-based images from the Cerro Tololo Inter-American Observatory (CTIO). For a fuller appreciation of its information content, explore the “zoomable” version: http://hubblesite.org/newscenter/archive/releases/2007/16/image/a/format/zoom/
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The Carinae Region: A Cauldron of Hot, Massive Stars
η Carinae
Trumpler 14
This spectacular montage was created to celebrate the 17th anniversary of Hubble’s deployment. It is composed of many separate exposures with Hubble’s Advanced Camera for Surveys (ACS) and ground-based images from the Cerro Tololo Inter-American Observatory (CTIO). For a fuller appreciation of its information content, explore the “zoomable” version: http://hubblesite.org/newscenter/archive/releases/2007/16/image/a/format/zoom/
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“S-Curve” from an FGS scan of a point source.
FGS1R: HST’s Interferometer That Can!E. Nelan, R.B. Makidon and L. Nagel (STScI)
HS
T F
ine
Guid
ance
Sen
sors Introduction
The unprecedented pointing precision required by the Hubble Space Telescope (HST) motivated the design of
the Fine Guidance Sensors (FGS). These are large field of view (FOV) interferometers that are able to track the
positions of luminous objects in HST’s focal plane with ~1 millisecond of arc (mas) precision. The FGS can
also scan an object’s interferogram with sub-mas resolution. These capabilities enable the FGS to perform as a
high-precision astrometric science instrument and high resolution interferometer which can be applied to a vari-
ety of topics and objectives, including:
• Visual orbits for binary systems with separations as small as 10 mas. Detection of duplicity down to 7 mas.
• Measuring the angular size of extended objects.
• Relative astrometry at the 0.2 mas level (mV < 14.5).
• 40 Hz relative photometry (e.g., flares, occultations) with milli-mag accuracy
ReferencesBenedict, G.F. et al. 1998, AJ, 116, 429.
Elliot, J.L., Strobel, D. F., Zhu, X., Wasserman, L. H., and Franz, O. G. 1998, DPS, 30.4901.
Harrison, T.E. et al. ApJ, 515, L93.
Lattanzi, M.G., Munari, U., Whitelock, P.A., and Feast, M.W. 1997, ApJ, 485, 328.
Niemela, V.S., Shara, M.S., Wallace, D.J., Zurek, D.R. and Moffat, A.F.J. 1998, AJ, 115, 2047.
Abramowicz-Reed, L. 1997, private communication.
Transfer Mode Observing
In Transfer Mode the FGS scans an object to obtain its interferometric fringes with sub-mas resolution. This is
conceptually equivalent to imaging an object with sub-mas pixels. This makes the FGS ideal for studying binary
systems and extended objects over a large magnitude range (3.0 < mV < 16.0).
Binary Systems
Angular Diameters
Actual WFPC2 and simulated FGS Observations of a 168 mas binary system.
Simulated WFPC2 and FGS Observations of a 70 mas binary system.
Although the binary in this exam-
ple is clearly resolved by the
WFPC2 Planetary Camera (PC)
(Niemela et al. 1999), the FGS
could measure the component sep-
aration and relative brightness with
greater accuracy (± 1 mas v.
± 30 mas).
Although a PC detection would be
questionable at 70 mas, the FGS
clearly isn’t challenged in detect-
ing duplicity and measuring sepa-
rations. Detections of duplicity
down to 7 mas are possible with
the FGS.
The FGS has been used successfully to determine the
angular diameters of non-point sources. the example given
in the figure at left shows the Transfer Function of a Mira-
type variable (Lattanzi et al. 1997) superposed on the S-
Curve of a point source. The extended source - a disk of
78 ± 2 mas - is clearly distinguishable from a point source.
In addition to stellar disks, the FGS has also been used to
determine the angular sizes of Active Galactic Nuclei
(AGNs), asteroids, and extragalactic star formation
regions.
Position Mode Observing
As an astrometer, the FGS can measure the relative positions of stars in its Field of View (FOV) with a per-
observation precision of ~ 1 mas. Key characteristics of observing in Position Mode include:
• A large (69 arcmin2) Field of View (FOV).
• A large dynamic range (3.0 < mV < 16.0).
• Binary and variable star astrometry.
• Down to 0.2 mas relative astrometry for multi-epoch observing programs (achievable in ~ 12 HST orbits)
In Position Mode, the FGS has been successfully used to measure astrometric parallaxes to a number of targets,
including the nearby dwarfs Proxima Centauri and Barnards Star (Benedict et al. 1998), and the dwarf novae
SS Aurigae, SS Cygni and U Geminorum (Harrison et al. 1998).
6.6
10.6
13.1
7.2
15.2
15.4
14.3
13.6
16.1
14.9
12.1
9.2
10.8
15.3
11.9
11.8
11.6
15.9
15.113.7
14.1
13.6
The FGS FOV and a “Typical” Astrometric Star Field.
In the above example, the science target is denoted by the central triangle, while astrometric reference stars are
denoted by circles. Magnitudes of individual objects are given beside each target. Note the magnitude range, from
mV = 6.6 to mV = 16.1.
Relative Photometry
While conducting Position Mode observations, FGS3 successfully captured a flare event on Proxima Centauri
(Benedict et al. 1998). In another series of observations, the FGS observed the occultation of a 10.6 magnitude
star by the Neptunian moon Triton (Elliot et al. 1998).
The absolute FGS photometric response has been stable to 2% over the past seven years (Abramowicz-Reed
1997). For relative photometry, on time scales of orbits, the FGS is stable to about 1 milli-magnitude at a rate of
40 Hz. This affords an opportunity for 0.1 to 0.2% time-series photometry for most tar gets.
Flare Outburst on Proxima Centauri Stellar Occultation by the Moon Triton
STScI is Operated by the Association of Universities for Research in Astronomy, Inc., for the National Aeronautics and Space Ad ministration.
Cycle 9 Call for Proposals
The HST Cycle 9 Call for Proposals will be released in June 1999, with a GO proposal deadline of Friday ,
10 Sep 1999 at 8:00PM EST. Propose early. Propose often. Propose wisely!
From the FGS Instrument Handbook 24
HD 93129A Trumpler 14
Palomar Digital Sky Survey
Component A is also a binary!
HD 93129A
HD 93129B
European Southern Observatory Science Release 0947 Very Large Telescope + Multi-Conjugate Adaptive Optics Demonstrator
ESO VLT: Aperture Mask with Adaptive Optics Sana et al. 2014 Astrophysical Journal Supplement
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NGC 3603 HST/ACS
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Outline
• Rachel Osten - cool stars • Alex Fullerton - massive stars • Jay Anderson – globular clusters
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Plan
(1) Globular Clusters before HST
(2) Globular Clusters with HST
(3) Globular Clusters with 25 years of HST
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Globular Clusters • “Textbook” simple stellar populations
– Formed stars early
– Single cloud, single metallicity, single age
– Not large enough to self-enrich
– Continue orbiting in spheroid of Galaxy
• Perfect fossil
laboratories
to evaluate
stellar evolution
GC
GC
GC
GC GC
NGC4013(NOAO) 29
ω Centauri
project-nightflight.net
Central Field
Early Release Field 30
http://hubblesite.org/newscenter/archive/releases/2010/28/ 31
http://hubblesite.org/newscenter/archive/releases/2010/28/ 32
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 33
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 34
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 35
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 36
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 37
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 38
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 39
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 40
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 41
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 42
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 43
What Astronomers see…
http://hubblesite.org/newscenter/archive/releases/2010/28/ 44
What Astronomers see…
1) Main
Sequence 2) SubGiant
Branch
3) Red Giant
Branch
4) Horizontal
Branch
5) White
Dwarf
Sequence
http://hubblesite.org/newscenter/archive/releases/2010/28/ 45
What Astronomers see…
Easy to identify stars… RGB
WDs
SGB
HB
MSTO
Red Dwarfs
BSs
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More metals
More Helium
Age
Red Giant Branch
A
B
C One line means: same age same metallicity same distance same small cloud
Stellar
Populations
“Isochrone”
“test of good photometry”
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Omega N6397 47T
Omega Cen NGC6397 47 Tuc
Extra sequences
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Plan
(1) Globular Clusters before HST
(2) Globular Clusters with HST
(3) Globular Clusters with 25 years of HST
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Globular Cluster or Dwarf Spheroidal?
Cambridge, UK 2001
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Stellar
Populations
More metals
More Helium
Age
Inversion!
More metals
metal poor
intermediate
metal rich
Red Giant Branch
Similar to galaxies…
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Is Omega Cen a GC? Could the textbook globular cluster not be one?
47Tuc
N2808
N6656 N6388
OmCen
®
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Is Omega Cen a globular?
Are there any globular clusters? Questions to answer: 1) How does the enrichment happen? 2) Why are they all so different? 3) What connection is there between clusters and galaxies? 4) Any relevance for star formation going on today?
NGC2808
NGC6652
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Plan
(1) Globular Clusters before HST
(2) Globular Clusters with HST
(3) Globular Clusters with 25 years of HST
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GCs with Hubble Over Time
• Set up new experiments
– Probe deeper
– Probe more broadly
• Use new detectors
– Better sensitivity, resolution
– Better filter sets
• Things move!
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Anderson et al 2002
Initial 2-seq Discovery on
Main Sequence (WF/PC2)
Bellini 2014 (WFC3/UVIS)
Latest results all over the
diagram! 10 Seqs!
ω Centauri
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D’Antona 2005 (ACS)
Initial Discovery
Bellini et al in prep
(WFC3/UVIS)
NGC2808
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2002 ACS H-alpha
Motions in ω Centauri
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2015 WFC3/UVIS F606W
Motions in ω Centauri
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2015 WFC3/UVIS F606W
MOTIONS OVER 13 YEARS Motions in ω Centauri
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Proper
Motions
Important Qs • Formation hints
• Are GCs just little galaxies?
• Do they have medium-sized BHs?
• How did the big BHs form in big galaxies?
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Plan
(1) Globular Clusters before HST
(2) Globular Clusters with HST
(3) Globular Clusters with 25 years of HST
(4) Globular Clusters in the next 25 years…
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View to the Future: the James Webb Space Telescope
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View to the Future: the James Webb Space Telescope
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