Synergy between Earth 2.0 Telescope and Chinese Space Station Telescope

Wei Zhu (祝伟)

Canadian Institute for Theoretical Astrophysics \(\longrightarrow\) Tsinghua University

Chinese Space Station Telescope

(CSST, Xuntian 巡天): China's HST

• Telescope: 2m space telescope in the same orbit as the Chinese Space Station (so serviceable); 2023/2024 launch.
• Instruments: Survey Camera (SC), Terahertz Receiver (THz), Multichannel Imager (MCI), Integral Field Spectrograph (IFS), Cool-Planet Imaging Coronagraph (CPIC).
• Mission: wide-area multiband imaging & slitless spectroscopic survey (7yr); other key programs & GO programs (2+yr).

CSST Survey Camera

• Multi-filter imaging & slitless spectroscopy
• Field of view: 1.1 deg\(^2\)
• Pixel size: 0.074"
• Tracking precision: 17 mas
• Image quality \(R_{\rm EE80}\): 0.15"@632.8 nm
• Point source sensitivity ~25.5\(^{\rm m}\) with 300s integration.

CSST Bulge Exoplanet Survey

• Lead by Ji-Lin Zhou (NJU) & Subo Dong (PKU), with collaborators from NJU, PKU, and Tsinghua.
• Transit & microlensing.
• Tentative field location: (Ra=17:56:51, Dec=-29:34:45).

CSST transit

CSST microlensing

• Tentative field location: (Ra=17:56:51, Dec=-29:34:45).
• Sun-angle & Moon-angle constraints \(\longrightarrow\) Observing window >20-40 min/(~95 min orbit) & fast-slew mode (\(0.35^\circ\)/s) to make use of the rest of the time.
• Survey duration: 3 months.
• Each pointing: 1 min exposure, 40 s readout & slew.
• Each block: 4 pointings (1.2 deg\(^2\)), 400 s.
• One complete field visit: 3 blocks (3.6 deg\(^2\)), 20 min.

CSST orbit data from Youhua Xu (NAOC)

A Tentative Survey Strategy

The "Small Star Oppurtunity"

• More small stars \(\longrightarrow\) more microlensing events.
• Smaller stars \(\longrightarrow\) sharper caustic crossing features \(\longrightarrow\) detecting lower-mass planets.

Roman

CSST

Left figure from Weicheng Zang, right figure from Sajadian & Ignace (2020)

• Expected yield (3 months, 3.6 deg\(^2\)):
  • ~100 cold exoplanets (1-10 AU);
  • ~40 free-floating planets (FFPs);
  • Transiting planets with \(P\lesssim30\) days.
• Each Roman microlensing campaign (72 days, 2 deg\(^2\)):
  • ~200 cold planets (Penny et al. 2019);
  • ~80 FFPs (Johnson et al. 2020);
  • \(\gtrsim10^4\) transiting planets (Montet et al. 2017).
  • Key component of the US$3.2B Roman telescope (\(\geq2026\)).

Survey Expected Yield

Figure from Penny et al. (2019)

CSST bulge survey & ET: Microlensing parallax

Image credit: NASA/JPL

0.01 AU (\(2\,R_\odot\))

Earth 2.0 Telescope

CSST (lens@7kpc)

CSST (lens@4kpc)

Planet-to-star mass ratio=\(10^{-5}\)

• CSST+ET can measure masses of FFPs (Weicheng's talk) and bound planets.

CSST bulge survey & ET: Lens flux measurements

• Search for potential hosts of lensing FFPs.
• Measure lens mass by combining lens flux and angular Einstein radius (from caustic crossings).
• Proper motion measurements, color magnitude diagram.

Images from Pietrukowicz et al. (2019)

CSST bulge survey & ET: Transit surveys

• Transit surveys of very different stellar populations may reveal the dependence of close-in planets on stellar properties.
• Previous transit surveys (e.g., K2, TESS) not designed for statistical studies.

Image credit: NASA/JPL

ET Field

CSST Bulge Survey

Summary

• CSST bulge survey:
  • 2m optical telescope @Leo
  • 3 months, ~3.6 deg\(^2\);
  • ~40 FFPs, ~100 cold exoplanets, and many close-in transiting planets.
• Synergy with ET:
  • Microlensing parallax & mass measurements of FFPs and bound planets;
  • Constrain the potential hosts of microlensing planets;
  • Transit surveys of stars under different environments.

Earth 2.0/CSST Microlensing

CSST Transit

Microlensing parallax

Microlensing parallax directly measures the lens mass (instead of mass ratio).

Spitzer team (incl. WZ), 2014-2019 (see also Dong et al. 2007)

1st exposure

2nd exposure

3rd exposure

4th exposure

• Each pointing: 1 min exposure, 40 s readout & slew.
• Each block: 4 pointings (1.2 deg\(^2\)), 400 s.
• Each complete field: 3 blocks (3.6 deg\(^2\)), 20 min.

1st exposure

A Tentative Survey Strategy

第1次曝光

第2次曝光

第3次曝光

第4次曝光