CSST and Earth 2.0 Telescope

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.

(effective FoV ~0.5 deg$^2$@grizy)

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

1st exposure

2nd exposure

3rd exposure

4th exposure

$1.1^\circ$

$0.2^\circ$

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)

CSST transit

CSST microlensing

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

CSST

KMTNet

Earth 2.0

Roman

Kepler

Spitzer

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.