Welcome to the AOP Open Repository

• The HASHTAG project II. Giant molecular cloud properties across the M31 disc

  National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing, 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China; School of Astronomy and Space Science, Nanjing University, Nanjing 210023, China; National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan; National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing, 100101, China; School of Astronomy and Space Science, Nanjing University, Nanjing 210023, China; Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Nanjing 210023, China; Cosmic Dawn centre (DAWN), Technical University of Denmark, DK2800 Kgs. Lyngby, Denmark; DTU-Space, Technical University of Denmark, Elektrovej 327, DK2800 Kgs. Lyngby, Denmark; National Astronomical Observatories, Chinese Academy of Sciences, A20 Datun Road, Chaoyang District, Beijing, 100101, China;; School of Physics, and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, UK;; School of Mathematical and Physical Sciences, Macquarie University, Balaclava Road, Sydney NSW 2109, Australia; Astrophysics and Space Technologies Research Centre, Macquarie University, Balaclava Road, Sydney NSW 2109, Australia; International Space Science Institute-Beijing, 1 Nanertiao, Zhongguancun, Hai Dian District, Beijing 100190, China; School of Physics, and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA, UK; Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, UK; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DB, UK;; National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588, Japan; Astronomical Science Program, The Graduate University for Advanced Studies SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; et al. (Monthly Notices of the Royal Astronomical Society, 2025-03-01)

  We present a study of giant molecular cloud (GMC) properties in the Andromeda galaxy (M31) using CO(3-2) data from the James Clerk Maxwell Telescope (JCMT) in selected regions across the disc and in the nuclear ring, and comparing them with CO(1-0) observations from the IRAM 30m telescope in the same regions. We find that GMCs in the centre of M31 generally exhibit larger velocity dispersions (σ) and sizes (R) compared to those in the disc, while their average surface density (Σ) and turbulent pressure (P<SUB>turb</SUB>) are lower. This low turbulent pressure in the central region is primarily due to the low density of molecular gas. The estimated GMC properties depend on the choice of CO transitions. Compared to CO(1-0), CO(3-2) exhibits smaller velocity dispersion and equivalent radius but higher surface density. These differences highlight the distinct physical conditions probed by different molecular gas tracers. We estimate the virial parameter α<SUB>vir</SUB>∝σ<SUP>2</SUP>R/Σ and find that most molecular clouds exhibit high values (α<SUB>vir</SUB> ~ 4 - 6) for both CO transitions, indicating that they are unbound. Furthermore, clouds in the nuclear ring display even larger α<SUB>vir</SUB> values of ≲ 100, suggesting that they may be highly dynamic, short-lived structures, although they could potentially achieve equilibrium under the external pressure exerted by the surrounding interstellar medium.
• PAMS: The Perseus Arm Molecular Survey-I. Survey description and first results

  School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK;; School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK; Physics Department, University of Bath, Claverton Down, Bath BA2 7AY, UK; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DB, UK;; Astrophysics Research Institute, Liverpool John Moores University, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK; Cardiff Hub for Astrophysics Research and Technology, School of Physics and Astronomy, Cardiff University, Queens Buildings, Cardiff CF24 3AA, UK;; Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada; Centre for Astrophysics and Planetary Science, University of Kent, Canterbury CT2 7NH, UK;; Department of Physics, Aberystwyth University, Penglais, Aberystwyth, Ceredigion SY23 3BZ, UK;; RAL Space, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, UK; Rigby, Andrew J.; et al. (Monthly Notices of the Royal Astronomical Society, 2025-03-01)

  The external environments surrounding molecular clouds vary widely across galaxies such as the Milky Way, and statistical samples of clouds are required to understand them. We present the Perseus Arm Molecular Survey (PAMS), a James Clerk Maxwell Telescope (JCMT) survey combining new and archival data of molecular-cloud complexes in the outer Perseus spiral arm in <inline-formula><tex-math id=TM0001 notation=LaTeX>$^{12}$</tex-math></inline-formula>CO, <inline-formula><tex-math id=TM0002 notation=LaTeX>$^{13}$</tex-math></inline-formula>CO, and C<inline-formula><tex-math id=TM0003 notation=LaTeX>$^{18}$</tex-math></inline-formula>O (J = 3-2). With a survey area of <inline-formula><tex-math id=TM0005 notation=LaTeX>$\sim$</tex-math></inline-formula>8 deg<inline-formula><tex-math id=TM0006 notation=LaTeX>$^2$</tex-math></inline-formula>, PAMS covers well-known complexes such as W3, W5, and NGC 7538 with two fields at <inline-formula><tex-math id=TM0007 notation=LaTeX>$\ell \approx 110^{\circ }$</tex-math></inline-formula> and <inline-formula><tex-math id=TM0008 notation=LaTeX>$\ell \approx 135^{\circ }$</tex-math></inline-formula>. PAMS has an effective resolution of 17 arcsec, and rms sensitivity of <inline-formula><tex-math id=TM0009 notation=LaTeX>$T_\mathrm{mb}= 0.7$</tex-math></inline-formula>-1.0 K in 0.3 km s<inline-formula><tex-math id=TM0010 notation=LaTeX>$^{-1}$</tex-math></inline-formula> channels. Here we present a first look at the data, and compare the PAMS regions in the Outer Galaxy with Inner Galaxy regions from the CO Heterodyne Inner Milky Way Plane Survey (CHIMPS). By comparing the various CO data with maps of H<inline-formula><tex-math id=TM0011 notation=LaTeX>$_2$</tex-math></inline-formula> column density from Herschel, we calculate representative values for the CO-to-H<inline-formula><tex-math id=TM0012 notation=LaTeX>$_2$</tex-math></inline-formula> column-density X-factors, which are <inline-formula><tex-math id=TM0014 notation=LaTeX>$X_\mathrm{^{12}CO\, (3-2)}$</tex-math></inline-formula><inline-formula><tex-math id=TM0015 notation=LaTeX>$\, =4.0\times 10^{20}$</tex-math></inline-formula> and <inline-formula><tex-math id=TM0016 notation=LaTeX>$X_\mathrm{^{13}CO\, (3-2)}$</tex-math></inline-formula><inline-formula><tex-math id=TM0017 notation=LaTeX>$\, =4.0\times 10^{21}$</tex-math></inline-formula> cm<inline-formula><tex-math id=TM0018 notation=LaTeX>$^{-2}$</tex-math></inline-formula> (K km s<inline-formula><tex-math id=TM0019 notation=LaTeX>$^{-1}$</tex-math></inline-formula>)<inline-formula><tex-math id=TM0020 notation=LaTeX>$^{-1}$</tex-math></inline-formula> with a factor of 1.5 uncertainty. We find that the emission profiles, size-linewidth, and mass-radius relationships of <inline-formula><tex-math id=TM0021 notation=LaTeX>$^{13}$</tex-math></inline-formula>CO-traced structures are similar between the Inner and Outer Galaxy. Although PAMS sources are slightly more massive than their Inner Galaxy counterparts for a given size scale, the discrepancy can be accounted for by the Galactic gradient in gas-to-dust mass ratio, uncertainties in the X-factors, and selection biases. We have made the PAMS data publicly available, complementing other CO surveys targeting different regions of the Galaxy in different isotopologues and transitions.
• Stellar X-Ray Variability and Planetary Evolution in the DS Tucanae System

  Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA; Geneva Observatory, University of Geneva, Chemin Pegasi 51b, CH-1290 Versoix, Switzerland; Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Armagh Observatory and Planetarium, College Hill, Armagh, NIR BT61 9DG, UK; King, George W.; Corrales, Lía R.; Bourrier, Vincent; Dos Santos, Leonardo A.; et al. (The Astrophysical Journal, 2025-02-01)

  We present an analysis of four Chandra observations of the 45 Myr old DS Tuc binary system. We observed X-ray variability of both stars on timescales from hours to months, including two strong X-ray flares from star A. The implied flaring rates are in agreement with past observations made with XMM-Newton, though these rates remain imprecise due to the relatively short total observation time. We find a clear, monotonic decline in the quiescent level of the star by a factor of 1.8 across 8 months, suggesting stellar variability that might be due to an activity cycle. If proven through future observations, DS Tuc A would be the youngest star for which a coronal activity cycle has been confirmed. The variation in our flux measurements across the four visits is also consistent with the scatter in empirical stellar X-ray relationships with Rossby number. In simulations of the possible evolution of the currently super-Neptune-sized planet DS Tuc A b, we find a range of scenarios for the planet once it reaches a typical field age of 5 Gyr, from Neptune size down to a completely stripped super-Earth. Improved constraints on the planet's mass in the future would significantly narrow these possibilities. We advocate for further Chandra observations to better constrain the variability of this important system.
• Linear and non-linear models for large-amplitude radial pulsation in faint blue stars (BLAPs)

  Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, Northern Ireland;; Jeffery, C. S. (Monthly Notices of the Royal Astronomical Society, 2025-03-01)

  The recent discovery of large-amplitude pulsations in faint blue stars (BLAPs) provides both challenges for stellar pulsation theory and opportunities to explore the late evolution of low-mass stars. This paper explores the radial-mode stability of stars across parameter space occupied by BLAPs. Models are constructed for homogeneous stellar envelopes and are agnostic of evolution. Linear non-adiabatic models demonstrate the major requirement for pulsations to be enrichment of iron and nickel in the driving zone to a few times the solar abundance. There is no constraint on mass. Non-linear models demonstrate that BLAP pulsations will be of large amplitude and will show strong shocks at minimum radius. A variety of light-curve shapes are found across the BLAP instability strip, accounting for the variety observed. Linearised period relations are derived from the non-linear models. The phase of maximum luminosity relative to minimum radius is correlated with effective temperature ( T<SUB>eff</SUB>), preceding for cool stars and following for hot stars, and split if close to minimum radius. In both linear and non-linear cases, most models pulsate in the fundamental mode (F). First-overtone (1H) pulsations are excited on the low luminosity blue side of the instability region and become more prevalent at higher mass. The period ratio P<SUB>1H</SUB>/P<SUB>F</SUB> = 0.81 contrasts with the classical Cepheid value (0.70 - 0.75). The transition from F to 1H mode pulsations follows a period-mass relation; the F-mode pulsators adjacent to the transition show a reverse shock. At high T<SUB>eff</SUB> some non-linear models show unstable overtone modes up to 5H and multi-mode behaviour. The linear and non-linear analyses concur on the red-edge of the instability region, but the non-linear blue edge is hotter.
• 

  Stellar X-Ray Variability and Planetary Evolution in the DS Tucanae System

  Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA; Geneva Observatory, University of Geneva, Chemin Pegasi 51b, CH-1290 Versoix, Switzerland; Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Armagh Observatory and Planetarium, College Hill, Armagh, NIR BT61 9DG, UK; King, George W.; Corrales, Lía R.; Bourrier, Vincent; Dos Santos, Leonardo A.; et al. (The Astrophysical Journal, 2025-02-01)

  We present an analysis of four Chandra observations of the 45 Myr old DS Tuc binary system. We observed X-ray variability of both stars on timescales from hours to months, including two strong X-ray flares from star A. The implied flaring rates are in agreement with past observations made with XMM-Newton, though these rates remain imprecise due to the relatively short total observation time. We find a clear, monotonic decline in the quiescent level of the star by a factor of 1.8 across 8 months, suggesting stellar variability that might be due to an activity cycle. If proven through future observations, DS Tuc A would be the youngest star for which a coronal activity cycle has been confirmed. The variation in our flux measurements across the four visits is also consistent with the scatter in empirical stellar X-ray relationships with Rossby number. In simulations of the possible evolution of the currently super-Neptune-sized planet DS Tuc A b, we find a range of scenarios for the planet once it reaches a typical field age of 5 Gyr, from Neptune size down to a completely stripped super-Earth. Improved constraints on the planet's mass in the future would significantly narrow these possibilities. We advocate for further Chandra observations to better constrain the variability of this important system.

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