Recipes

Noise-to-Signal Ratio Estimates

PLATO's proposal software, with its built-in Call for Proposals Toolkit (CfP), provides an easy‑to‑use interface to estimate the expected photometric Noise‑to‑Signal Ratio (NSR) for standard stellar targets up to PLATO magnitude (Pmag) < 15. Some Guest Observers may wish to propose observations of fainter stars, objects without Pmag, or non‑stellar sources, which may require more tailored NSR estimations. To provide new proposers with a starting point for further exploration, this page describes two available community methods: 

• The Quick noise model described in section 3.2 of Cabrera et al. (2026), which uses as input the target flux integrated over the PLATO wavelength range (500-1000 nm). This model includes spacecraft jitter, background and read out noise, and photon noise. 
• PlatoSim: The PLATO Simulator (PlatoSim) is an end-to-end tool for simulating realistic observations from the PLATO mission. It generates time series of CCD images, modelling the stellar field, spacecraft systematics, jitter, camera optics, CCD electronics, and key sources of noise. It includes modules that can help to generate noise estimates across PLATO’s focal plane. PlatoSim simulations are particularly helpful to analyse the impact of contaminants in the NSR, which may be significant especially for lower magnitude stars. 

Below are several guidelines regarding the usage of these methods for various types of objects. 

Stars with Pmag ≤ 15

The CfP NSR calculator is trained on the full PLATO Input Catalogue (PIC), including the science calibration and validation sample (scvPIC), which covers a broad range of stellar types up to Pmag ≤ 15. When users upload their target lists in the CfP, the tool automatically uses the entered Pmag and PLATO’s noise model to compute NSR values within the proposal software.

For most science cases, these estimates are fully sufficient. However, as the accuracy of the CfP predictions decreases for stars of specral types different from those of the stars in the PIC (e.g., OB stars), proposers may use the Quick noise model for comparison, or PlatoSim for a deeper analysis. 

Stars with Pmag > 15 or No Pmag Available

For fainter stars (Pmag > 15), or for stars that do not currently have a listed Pmag, proposers may need to complement the CfP with the Quick noise model or with tailored simulations. Additionally, published noise–magnitude curves may provide helpful reference points in the fainter regime (see e.g., Jannsen et al., 2025).

When using PlatoSim, a practical starting point is to provide an approximate value of Pmag; Gaia’s G magnitude generally provides a reasonable proxy.

Non‑Stellar Objects (SSOs, Transients, AGN, Galaxies, etc.)

For non‑stellar targets that can still be treated as point sources, and for which no Pmag value is available, a rough first‑order estimate may be obtained from the Quick noise model. PlatoSim provides more detailed results by using the Gaia G magnitude as a proxy.

The following figure provides the NSR determinations for the N-CAMs by Jannsen (in preparation) for a Quasar catalogue for beginning-of-life conditions. The left panel displays the camera level NSR estimates colour-coded after (distorted) gnomonic radial distance from the optical axis. The figure shows the theoretical noise prediction (orange solid line), constituted by a jitter noise limit (neglectable here), photon noise limit (pink dashed-dotted line), and the sky/read noise limit (pink dotted line). The right panel displays mission level NSR estimates colour-coded after the number of cameras visibility. The black points in both panels are Quasars with SPR>0.01. (Please cite Jannsen et al., in preparation, if you use this plot for your proposal). 

For extended sources, where the flux is spread over several PLATO pixels, users should consider both surface brightness and the object’s angular size relative to PLATO’s aperture. In such cases, it may be useful to treat each imagette as sampling a local surface‑brightness element rather than a single point source, and to run representative patch simulations to approximate the effective noise.

Any targets with Pmag ≳ 17

It is not generally recommended to propose for observations of targets with Pmag ≳ 17 because this is close to PLATO's ultimate detection limit. The corresponding predictions of the system behaviour become significantly less accurate due to the impact of charge transfer inefficiency and digitalisation noise. Proposers wishing to observe targets with Pmag ≳ 17 should foresee a clear feasibility study to convince the TAC that their scientific question(s) can be answered from PLATO observations, even if using it beyond its foreseen capacity.