Search Publications
Using old and new approaches: determining physical properties of brown dwarfs with empirical relations and machine learning models
Best, William M. J.; Feeser, S. Jean
We investigate applications of machine learning models to directly infer physical properties of brown dwarfs from their photometry and spectra using THE CANNON. We demonstrate that absolute magnitudes, spectral types, and spectral indices can be determined from low-resolution SpeX prism spectra of L and T dwarfs without trigonometric parallax meas…
Long-term variation of coronal holes latitudinal distribution
Chargeishvili, B. B.; Maghradze, D. A.; Japaridze, D. R. +2 more
We study the evolution of the latitudinal distribution of coronal holes using the Solar and Heliospheric Observatory (SOHO)/Extreme ultraviolet Imaging Telescope (EIT) 195 Å data from 1996 May to 2020 April. To measure the presence of coronal holes at a given latitude, we use the presence factor, which estimates the length of an object along a giv…
Be, V, and Cu in the halo star CS 31082-001 from near-UV spectroscopy
Spite, M.; Evans, C. J.; Barbuy, B. +5 more
The 'First Stars' programme revealed the metal-poor halo star CS 31082-001 to be r-process and actinide rich, including the first measurement of a uranium abundance for an old star. To better characterize and understand such rare objects, we present the first abundance estimates of three elements (Be, V, Cu) for CS 31082-001 from analysis of its n…
Decade-long time-monitoring of candidate luminous blue variable stars in the two very metal-deficient star-forming galaxies DDO 68 and PHL 293B
Thuan, T. X.; Izotov, Y. I.; Guseva, N. G.
We have studied the spectral time variations of candidate luminous blue variable (cLBV) stars in two low-metallicity star-forming galaxies, DDO 68 and PHL 293B. The LBV in DDO 68, located in H II region #3, shows an outburst, with an increase of more than 1000 times in H α luminosity during the period 2008-2010. The broad emission of the H I and H…
ALMA's view of the M-dwarf GSC 07396-00759's edge-on debris disc: AU Mic's coeval twin
Kral, Quentin; Murphy, Simon J.; Wyatt, Mark C. +7 more
We present new ALMA Band 7 observations of the edge-on debris disc around the M1V star GSC 07396-00759. At ~20 Myr old and in the β Pictoris Moving Group along with AU Mic, GSC 07396-00759 joins it in the handful of low-mass M-dwarf discs to be resolved in the sub-mm. With previous VLT/SPHERE scattered light observations, we present a multiwavelen…
Planetary nebulae with Wolf-Rayet-type central stars - IV. NGC 1501 and its mixing layer
Guerrero, M. A.; Toalá, J. A.; Todt, H. +4 more
Theory predicts that the temperature of the X-ray-emitting gas (~106 K) detected from planetary nebulae (PNe) is a consequence of mixing or thermal conduction when in contact with the ionized outer rim (~104 K). Gas at intermediate temperatures (~105 K) can be used to study the physics of the production of X-ray-em…
Investigating a predicted metallicity [Fe/H] variation in the Type II Globular Cluster NGC 362
Sarajedini, Ata; Monaco, L.; Geisler, D. +4 more
NGC 362 is a non-common Type II Galactic globular cluster, showing a complex pseudo two-colour diagram or 'chromosome map'. The clear separation of its stellar populations in the colour-magnitude diagram and the distribution of the giant stars in the chromosome map strongly suggests that NGC 362 could host stars with both cluster-nominal, as well …
The missing radial velocities of Gaia: Blind predictions for DR3
Widmark, Axel; Naik, Aneesh P.
While Gaia has observed the phase space coordinates of over a billion stars in the Galaxy, in the overwhelming majority of cases it has only obtained five of the six coordinates, the missing dimension being the radial (line-of-sight) velocity. Using a realistic mock data set, we show that Bayesian neural networks are highly capable of 'learning' t…
Counterparts of candidate dusty starbursts at z > 6
Yan, Haojing; Ling, Chenxiaoji; Ma, Zhiyuan
We present an analysis of the optical-to-near-infrared (IR) counterparts of a sample of candidate dusty starbursts at z > 6. These objects were pre-selected based on the rising trend of their far-IR-to-sub-millimeter spectral energy distributions and the fact that they are radio-weak. Their precise positions are available through millimeter and…
A search for period changes of eight short-period Type II Cepheids
Whitelock, Patricia A.; Kniazev, Alexei Y.; Yacob, Alemiye M. +2 more
In this study, we investigate the period changes of eight short-period Type II Cepheids of the BL Her subtype, i.e. with periods in the 1-4 d range. The O - C diagrams for these stars are constructed using all suitable observational data from ground and space surveys. This spans a time interval of over one century and includes digitized photograph…