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• Speaker: Paola Pinilla (MSSL)
• Tuesday 04 June 2024, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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• Speaker: Florian Lienhard (Zurich)
• Tuesday 30 April 2024, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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• Speaker: Emily Sandford (Cavendish)
• Tuesday 14 May 2024, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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arXiv:2304.06144v2 Announce Type: replace Abstract: We present analysis of NuSTAR X-ray observations of three AGN that were identified as candidate subparsec binary supermassive black hole (SMBH) systems in the Catalina Real-Time Transient Survey based on apparent periodicity in their optical light curves. Simulations predict that close-separation accreting SMBH binaries will have different X-ray spectra than single accreting SMBHs. We previously observed these AGN with Chandra and found no differences between their low energy X-ray properties and the larger AGN population. However some models predict differences to be more prominent at energies higher than probed by Chandra. We find that even at the higher energies probed by NuSTAR, the spectra of these AGN are indistinguishable from the larger AGN population. This could rule out models predicting large differences in the X-ray spectra in the NuSTAR bands. Alternatively, it might mean that these three AGN are not binary SMBHs.

arXiv:2403.18954v1 Announce Type: new Abstract: Supernova (SN) H0pe is a gravitationally lensed, triply-imaged, Type Ia SN (SN Ia) discovered in James Webb Space Telescope imaging of the PLCK G165.7+67.0 cluster of galaxies. Well-observed multiply-imaged SNe provide a rare opportunity to constrain the Hubble constant ($H_0$), by measuring the relative time delay between the images and modeling the foreground mass distribution. SN H0pe is located at $z=1.783$, and is the first SN Ia with sufficient light curve sampling and long enough time delays for an $H_0$ inference. Here we present photometric time-delay measurements and SN properties of SN H0pe. Using JWST/NIRCam photometry we measure time delays of $\Delta t_{ab}=-116.6^{+10.8}_{-9.3}$ and $\Delta t_{cb}=-48.6^{+3.6}_{-4.0}$ observer-frame days relative to the last image to arrive (image 2b; all uncertainties are $1\sigma$), which corresponds to a $\sim5.6\%$ uncertainty contribution for $H_0$ assuming $70 \rm{km s^{-1} Mpc^{-1}}$. We also constrain the absolute magnification of each image to $\mu_{a}=4.3^{+1.6}_{-1.8}$, $\mu_{b}=7.6^{+3.6}_{-2.6}$, $\mu_{c}=6.4^{+1.6}_{-1.5}$ by comparing the observed peak near-IR magnitude of SN H0pe to the non-lensed population of SNe Ia.

arXiv:2403.18894v1 Announce Type: new Abstract: In recent years, high-resolution transmission spectroscopy in the near-infrared has led to detections of prominent molecules in several giant exoplanets on close-in orbits. This approach has traditionally relied on the large Doppler shifts of the planetary spectral lines induced by the high velocities of the close-in planets, which were considered necessary for separating them from the quasi-static stellar and telluric lines. In this work we demonstrate the feasibility of high-resolution transmission spectroscopy for chemical detections in atmospheres of temperate low-mass exoplanets around M dwarfs with low radial velocity variation during transit. We pursue this goal using model injection and recovery tests with H- and K- band high-resolution spectroscopy of the temperate sub-Neptune TOI-732 c, observed using the IGRINS spectrograph on Gemini-S. We show that planetary signals in transit may be recovered when the change in the planet's radial velocity is very small, down to sub-pixel velocities. This is possible due to the presence of the planetary signal in only a subset of the observed spectra. A sufficient number of out-of-transit spectra can create enough contrast between the planet signal and telluric/stellar contaminants that the planet signal does not constitute a principal component of the time-series spectra and can therefore be isolated using PCA-based detrending without relying on a significant Doppler shift. We additionally explore novel metrics for finding such signals, and investigate trends in their detectability. Our work extends the scope of high-resolution transmission spectroscopy and creates a pathway towards the characterisation of habitable sub-Neptune worlds with ground-based facilities.

arXiv:2403.18891v1 Announce Type: new Abstract: The study of temperate sub-Neptunes is the new frontier in exoplanetary science. A major development in the past year has been the first detection of carbon-bearing molecules in the atmosphere of a temperate sub-Neptune, K2-18 b, a possible Hycean world, with the James Webb Space Telescope (JWST). The JWST is poised to characterise the atmospheres of several other such planets with important implications for planetary processes in the temperate regime. Meanwhile, ground-based high-resolution spectroscopy has been highly successful in detecting chemical signatures of giant exoplanets, though low-mass planets have remained elusive. In the present work, we report the atmospheric reconnaissance of a temperate sub-Neptune using ground-based high-resolution transmission spectroscopy. The long orbital period and the low systemic velocity results in a low planetary radial velocity during transit, making this system a valuable testbed for high-resolution spectroscopy of temperate sub-Neptunes. We observe high-resolution time-series spectroscopy in the H- and K-bands during the planetary transit with the IGRINS instrument (R$\sim$45,000) on Gemini-South. Using observations from a single transit we find marginal evidence (2.2$\sigma$) for the presence of methane (CH$_4$) in the atmosphere and no evidence for ammonia (NH$_3$) despite its strong detectability for a cloud-free H$_2$-rich atmosphere. We assess our findings using injection tests with different atmospheric scenarios, and find them to be consistent with a high CH$_4$/NH$_3$ ratio and/or the presence of high-altitude clouds. Our results demonstrate the capability of Gemini-S/IGRINS for atmospheric characterization of temperate sub-Neptunes, and the complementarity between space- and ground-based facilities in this planetary regime.

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Hubble Finds a Field of Stars This image from the NASA/ESA Hubble Space Telescope shows a globular cluster called NGC 1651. ESA/Hubble & NASA, L. Girardi, F. Niederhofer

This image from the NASA/ESA Hubble Space Telescope shows a globular cluster called NGC 1651. Like another recent globular cluster image, NGC 1651 is about 162,000 light-years away in the largest and brightest of the Milky Way’s satellite galaxies, the Large Magellanic Cloud (LMC). One notable feature of this image: the roughly 120-light-year diameter globular cluster nearly fills the entire frame. In contrast, other Hubble images feature entire galaxies – which can be tens or hundreds of millions of light-years in diameter – that also more or less fill the whole image.

A common misconception is that Hubble and other large telescopes observe wildly differently sized celestial objects by zooming in on them, as one would with a specialized camera here on Earth. While small telescopes might have the option to zoom in and out to a certain extent, large telescopes do not. Each telescope’s instrument has a fixed ‘field of view’ (the size of the region of sky that it can observe in a single observation). For example, the ultraviolet/visible light channel of Hubble’s Wide Field Camera 3 (WFC3), the channel and instrument that collected the data used in this image, has a field of view roughly one twelfth the diameter of the Moon as seen from Earth. When WFC3 makes an observation, its field of view is the size of the region of sky that it can observe.

The reason that Hubble can observe objects of such wildly different sizes is two-fold. First, the distance to an object will determine how big it appears from Earth, so entire galaxies that are relatively far away might take up the same amount of space in the sky as a globular cluster like NGC 1651 that is relatively close by. In fact, there’s a distant spiral galaxy lurking in this image, directly left of the cluster – though undoubtedly much larger than this star cluster, it appears small enough here to blend in with foreground stars! Secondly, images processors can stitch together multiple images spanning different parts of the sky into a mosaic to create a single image of objects that are too big for Hubble’s field of view.

Text credit: European Space Agency (ESA)

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Media Contact:

Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, MD
claire.andreoli@nasa.gov

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Details Last Updated Mar 29, 2024 Editor Andrea Gianopoulos Related Terms

• Astrophysics
• Astrophysics Division
• Goddard Space Flight Center
• Hubble Space Telescope
• Missions
• Star Clusters
• Stars
• The Universe

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Title to be confirmed

Abstract not available

• Speaker: Tsevi Mazeh (Tel Aviv)
• Friday 03 May 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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arXiv:2403.18000v1 Announce Type: new Abstract: Obtaining reliable distance estimates to gas clouds within the Milky Way is challenging in the absence of certain tracers. The kinematic distance approach has been used as an alternative, derived from the assumption of circular trajectories around the Galactic centre. Consequently, significant errors are expected in regions where gas flow deviates from purely circular motions. We aim to quantify the systematic errors that arise from the kinematic distance method in the presence of a Galactic potential that is non-axisymmetric. We investigate how these errors differ in certain regions of the Galaxy and how they relate to the underlying dynamics. We perform 2D isothermal hydrodynamical simulation of the gas disk with the moving-mesh code Arepo, adding the capability of using an external potential provided by the Agama library for galactic dynamics. We introduce a new analytic potential of the Milky Way, taking elements from existing models and adjusting parameters to match recent observational constraints. We find significant errors in the kinematic distance estimate for gas close to the Sun, along sight lines towards the Galactic centre and anti-centre, and significant deviations associated with the Galactic bar. Kinematic distance errors are low within the spiral arms as gas resides close to local potential minima and the resulting line-of-sight velocity is close to what is expected for an axisymmetric potential. Interarm regions exhibit large deviations at any given Galactic radius. This is caused by the gas being sped up or slowed down as it travels into or out of the spiral arm. We are able to define 'zones of avoidance' in the lv-diagram, where the kinematic distance method is particularly unreliable and should only be used with caution. We report a power law relation between the kinematic distance error and the deviation of the project line-of-sight velocity from circular motion.

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