arXiv subjects

Yanbo Pan

Publications and source records attributed to Yanbo Pan.

3 recordsLinked to original sources

arXiv2026

JWST MEP - A World Under Spotty Starlight: Detection of CO2 and H2O in the Hot Saturn WASP-52b with JWST NIRSpec G395H

Exoplanets orbiting active stars offer distinct challenges for atmospheric characterization with the JWST. Among such worlds, the hot Saturn WASP-52b (Teq $\sim$ 1300 K) orbits an active K-dwarf that complicates transmission spectroscopy via stellar contamination. Here, we present the first JWST NIRSpec G395H (2.8-5.2 $μ$m) limb-averaged transmission spectrum of WASP-52b obtained through the JWST Morning/Evening Program (GO-3969), which aims to measure limb asymmetries across a sample of hot giant exoplanets. Our spectrum reveals the first detection of CO2 in WASP-52b's atmosphere (ln B = 54 / >10$σ$), with a retrieved abundance of log CO2 = -5.09 (+1.09/-1.14), and confirmation of H2O (ln B = 5.9 / $\sim$3-4$σ$), with an abundance of log H2O = -3.41 (+1.04/-1.04). We find a steep near-infrared slope that cannot be explained solely by H2O absorption, necessitating unocculted starspots (ln B = 5.7 / $\sim$3-4$σ$), though with properties that vary across our data reductions. The shape and amplitude of the molecular bands additionally suggest high-altitude (<10 mbar) inhomogeneous clouds covering $\approx$40 $\pm$ 20% of the terminator (ln B = 1.9 / $\sim$2.5$σ$), which provides evidence for the morning-evening terminator differences that are consensus predictions of general circulation models. WASP-52b's atmospheric metallicity can be sub-solar, solar, or super-solar, due to order-of-magnitude uncertainties in the molecular abundances caused by degeneracies between compositions, clouds, and starspots. However, chemical equilibrium retrievals provide a similar statistical fit while favoring a tighter constraint with a super-solar metallicity (M/H = 14.8 (+12.1/-5.9) $\times$ solar). These results highlight that chemical detections and aerosol properties may still be recovered for planets orbiting active stars via transmission spectroscopy.

astro-ph.EP↗

arXiv2026

From observing strategies to velocity dispersion bias: forward modeling unresolved binaries in ultra-faint dwarf galaxies

Ultra-faint dwarf galaxies (UFDs) in the Milky Way are ideal probes of low-mass galaxy formation and dark matter because they are highly dark-matter dominated. In the lowest-mass systems, however, unresolved binary orbital motion complicates dynamical mass estimates by inflating measured velocity dispersions and biasing the interpretation of the inferred masses. We develop a flexible forward-modeling pipeline, the Binary Observation Simulator, to generate mock multi-epoch radial-velocity observations of binary populations in dwarf galaxies and to quantify how binary-induced biases depend on both galaxy properties and observing strategy. We generate mock samples spanning true velocity dispersion of $σ_{\rm true}\sim0.75$-$3.5$ km/sec, binary fractions of $0.1$-$0.9$, and multi-epoch baselines of up to $10$ yr. We find that, while multi-epoch monitoring reduces the binary-induced bias, residual contamination remains significant for low-mass halos: even a $10$-yr baseline can leave $\sim10$-$120\%$ relative bias for systems with $σ_{\rm true}\lesssim1$ km/sec. We also note that small sample sizes ($\lesssim20$) introduce substantial stochastic scatter in the recovered dispersions, sometimes masking the expected improvement from longer observational baselines. Applying the framework to the real $\sim17$-yr Bootes I observing record reproduces the literature velocity dispersions, yields an empirical correction conditioned on that cadence, and shows that redistributing the same observations onto half the number of stars would have removed roughly half of the residual binary bias. These results emphasize that robust dispersion estimates for the faintest dwarfs require forward modeling of both binary populations and survey cadence.

astro-ph.GA↗

arXiv2024

Transmission spectroscopy of WASP-52 b with JWST NIRISS: Water and helium atmospheric absorption, alongside prominent star-spot crossings

In the era of exoplanet studies with JWST, the transiting, hot gas giant WASP-52 b provides an excellent target for atmospheric characterization through transit spectroscopy. WASP-52 b orbits an active K-type dwarf recognized for its surface heterogeneities, such as star-spots and faculae, which offers challenges to atmospheric characterization via transmission spectroscopy. Previous transit observations have detected active regions on WASP-52 through crossing events in transit light-curves and via the spectral imprint of unocculted magnetic regions on transmission spectra. Here, we present the first JWST observations of WASP-52 b. Our JWST NIRISS/SOSS transit observation, obtained through the GTO 1201 Program, detects two clear spot-crossing events that deform the 0.6-2.8 $μ$m transit light-curves of WASP-52 b. We find that these two occulted spots combined cover about 2.4 % of the stellar surface and have temperatures about 400-500 K colder than the stellar photosphere. Our NIRISS/SOSS transmission spectrum is best-fit by an atmosphere with H$_2$O (10.8 $σ$), He (7.3 $σ$, with evidence of an escaping tail at $\sim$ 2.9 $σ$), hints of K (2.5 $σ$), and unocculted star-spots and faculae (3.6 $σ$). The retrieved H$_2$O abundance ($\log$ H$_2$O $\approx -4 \pm 1$) is consistent with a subsolar or solar atmospheric metallicity for two independent data reductions. Our results underscore the importance of simultaneously modelling planetary atmospheres and unocculted stellar heterogeneities when interpreting transmission spectra of planets orbiting active stars and demonstrate the necessity of considering different stellar contamination models that account for both cold and hot active regions.

astro-ph.EP↗