# Presentation: 045985

## The slides in this collection are all related and should be useful in preparing a presentation on SIM PlanetQuest.  Note, however, that there is some redundancy in the collection to allow users to choose slides best suited to their needs.

- November 23, 2004

## Stellar Evolution and the Distance Scale

- Distances in the Universe are uncertain because we don’t know the distances to “standard candle” stars
- SIM will measure accurate distances
- Masses of most stars are very poorly known
- SIM will measure accurate masses (to 1%) by using binary orbits
- Stellar evolution models can’t be further tested without accurate masses for ‘exotic objects’
- SIM will measure the masses of OB (massive) stars, supergiants, brown dwarfs

- November 23, 2004

## What More Can SIM Do?

- SIM can do far more than planet-finding!
- Two NAS decadal reviews have endorsed the fundamental astrophysics enabled by wide-angle astrometry
- 7 of 10 SIM Key projects are not aimed at finding exo-planets.
- This represents ~ 50% of the time allocated so far

- November 23, 2004

## How Do Stars Evolve?

- SIM will permit 1% mass measurements over the whole range of stellar types, including
- Black holes, OB stars to brown dwarfs, and white dwarfs.
- SIM can obtain precision masses for stars in  clusters covering a range of ages (1 Myr -- 5 Gyr) and a variety of metallicities
- SIM will use astrometry and photometry of micro-lensing events to determine physical properties of lensing stars

- November 23, 2004

## Sirius:  Proper Motion, True Orbits, Apparent Orbit

- November 23, 2004

## Actual Orbits of a Binary Star Pair

- November 23, 2004

## Using Gravitational Lenses to Probe ‘Dark Matter’

**Microlensing is the gravitational bending of light by chance alignments of stars**
**Events are detected by**
**Brightness enhancement (~days)**
**Astrometric perturbation (~weeks to months)**
**SIM enables measurement of lens distances**
**Observing program:**
**Ground-based *****photometric***** monitoring program of many stars in the galactic center **
**SIM performs *****astrometry***** on detected events as ‘targets of opportunity’**
**Apparent star position moves in a characteristic pattern with relatively large amplitude of ~100 μas**
**Symmetry of track ‘broken’ by Earth orbit motion due to lens parallax**
**Hence: distance to lens **
**Derive:  mass, distance, and velocity of the lensing object**

- (dark)
- lens

- SIM

- Background star

- Image

- November 23, 2004

## Slide 8

- November 23, 2004

## SIM Measures Distances to “Standard Candles”

- Period proportional to luminosity, but also metallicity
- Distances to galactic Cepheids to a Kpc and RR Lyraes in globular clusters can be measured to <1% accuracy, a key element in the cosmic distance scale

- November 23, 2004

## X-Ray Binary Studies

- “High-Mass” X-ray Binaries
- Primarily Narrow-Angle Program

- “Low-Mass” X-ray Binaries (LMXBs)
-  Wide-Angle Program

- November 23, 2004

## Low-Mass X-ray Binaries (LMXBs)

- Binary separations (a):
- - up to 50 microarcseconds (angular)
- - typically 0.01 AU (physical)
- Optical light:
- - dominated by companion in quiescence
- - dominated by accretion disk in outburst

- - X-rays and optical are correlated
- - Outbursts are unpredictable

- November 23, 2004

## LMXBs in the SIM PlanetQuest Program

- (17 targets)
- Category 2:  Transient in X-rays with Vquiescence brighter than 20
- (8 targets)
- Category 3:  Transient with Vquiescence fainter than 20 but Voutburst brighter than 20

- November 23, 2004

## Example #1:  GX 339-4

- Expected outburst behavior:
- - Outburst duration ~ 1 year
- - About two outbursts in a 5 year SIM mission
- Possible observing scenario:
- - Observations every 18 days (365 days/20) when the source is in outburst

- November 23, 2004

## Example #2:  GRO J1655-40

- One of the Category 2 sources (e.g., GRO J1655-40)

- Vquiescence = 17.3
- (companion dominates)
- Voutburst ~ 14.0
- (accretion disk dominates)
- The shift illustrated gives a
- measurement of the binary
- separation (a), which is
- expected to be about 24
- microarcseconds for
- GRO J1655-40.

- Scheduling:  The only constraint is to get two ~orthogonal baselines during an outburst.
- The observations should not be separated by more than about a week.

- November 23, 2004