The Transiting Exoplanet Survey Satellite, TESS, is currently carrying out an all-sky search for small planets transiting bright stars. In the first year of the TESS survey, steady progress was made ...in achieving the mission's primary science goal of establishing bulk densities for 50 planets smaller than Neptune. During that year, TESS's observations were focused on the southern ecliptic hemisphere, resulting in the discovery of three mini-Neptunes orbiting the star TOI-125, a V=11.0 K0 dwarf. We present intensive HARPS radial velocity observations, yielding precise mass measurements for TOI-125b, TOI-125c and TOI-125d. TOI-125b has an orbital period of 4.65 days, a radius of \(2.726 \pm 0.075 ~\mathrm{R_{\rm E}}\), a mass of \( 9.50 \pm 0.88 ~\mathrm{M_{\rm E}}\) and is near the 2:1 mean motion resonance with TOI-125c at 9.15 days. TOI-125c has a similar radius of \(2.759 \pm 0.10 ~\mathrm{R_{\rm E}}\) and a mass of \( 6.63 \pm 0.99 ~\mathrm{M_{\rm E}}\), being the puffiest of the three planets. TOI-125d, has an orbital period of 19.98 days and a radius of \(2.93 \pm 0.17~\mathrm{R_{\rm E}}\) and mass \(13.6 \pm 1.2 ~\mathrm{M_{\rm E}}\). For TOI-125b and TOI-125d we find unusual high eccentricities of \(0.19\pm 0.04\) and \(0.17^{+0.08}_{-0.06}\), respectively. Our analysis also provides upper mass limits for the two low-SNR planet candidates in the system; for TOI-125.04 (\(R_P=1.36 ~\mathrm{R_{\rm E}}\), \(P=\)0.53 days) we find a \(2\sigma\) upper mass limit of \(1.6~\mathrm{M_{\rm E}}\), whereas TOI-125.05 ( \(R_P=4.2^{+2.4}_{-1.4} ~\mathrm{R_{\rm E}}\), \(P=\) 13.28 days) is unlikely a viable planet candidate with upper mass limit \(2.7~\mathrm{M_{\rm E}}\). We discuss the internal structure of the three confirmed planets, as well as dynamical stability and system architecture for this intriguing exoplanet system.
We present the discovery and characterisation of two transiting planets
observed by \textit{TESS} in the light curves of the young and bright (V=9.67)
star HD73583 (TOI-560). We perform an intensive ...spectroscopic and photometric
space- and ground-based follow-up in order to confirm and characterise the
system. We found that HD73583 is a young ($\sim 500$~Myr) active star with a
rotational period of $12.08 \pm 0.11 $\,d, and a mass and radius of $ 0.73 \pm
0.02 M_\odot$ and $0.65 \pm 0.02 R_\odot$, respectively. HD73583 b
($P_b=6.3980420 _{ - 0.0000062 }^{+0.0000067}$ d) has a mass and radius of
$10.2 _{-3.1}^{+3.4} M_\oplus$ and$2.79 \pm 0.10 R_\oplus$, respectively, that
gives a density of $2.58 _{-0.81}^{ 0.95} {\rm g\,cm^{-3}}$. HD73583 c ($P_c=
18.87974 _{-0.00074 }^{+0.00086}$) has a mass and radius of $9.7_{-1.7} ^
{+1.8} M_\oplus$ and $2.39_{-0.09}^{+0.10} R_\oplus$, respectively, this
translates to a density of $3.88 _{-0.80}^{+0.91} {\rm g\,cm^{-3}}$. Both
planets are consistent with worlds made of a solid core surrounded by a
volatile envelope. Because of their youth and host star brightness, they both
are excellent candidates to perform transmission spectroscopy studies. We
expect ongoing atmospheric mass-loss for both planets caused by stellar
irradiation. We estimate that the detection of evaporating signatures on H and
He would be challenging, but doable with present and future instruments.
The drift ballooning mode (DBM) instability near the inner edge of the plasma sheet (IEPS) is studied further by including a nonstationary earthward flow and flow shear in the analysis. Both ...equatorial and off-equatorial regions are considered. It is found that the presence of a decelerated earthward flow destabilizes both the 34(-) and M(+) branches of the DBM in a large portion of the current sheet near the IEPS and substantially increases the growth rate of the instability. The flow shear in the premidnight sector causes the conventional ballooning mode to weakly subside, while it slightly enhances the growth rate for the Alfvenic ballooning mode. The combination of the earthward flow and flow shear makes both the Alfvenic ballooning mode and conventional ballooning mode grow much faster than they would without the flow, giving rise to coupled Alfvenic slow magnetosonic waves, field-aligned currents, and the formation of a current wedge. A synthesis of tail reconnection and cross-tail current disruption scenarios is proposed for the substorm global initiation process. We intend to use this global model to explain substorm expansion onsets occurring under the southward IMF condition. (Author)
The MHD drift ballooning mode (DBM) instability near the inner edge of the near-Earth plasma sheet is studied by using both the one-fluid generalized progressing wave expansion method and the ...two-fluid approach. It is found that in the frame of reference at rest relative to the bulk plasma the DBM may become a purely growing mode in two distinct circumstances, which, for convenience, are called the DBM1 and DBM2, respectively. The B threshold for the DBM1 is identical with that derived by Ohtani and Tamao (1993) and Southwood and Kivelson (1987), while the criterion of the DBM2 covers that of Miura et al. (1989). Comparisons of the theory with GEOS 2 data show that the DBM2 is more easily excited in the late substorm growth phase. There is considerable evidence that the DBM is generated at expansion onsets. The characteristic features of magnetic field dipolarization can be interpreted in terms of the development of the DBM. (Author)
We present the discovery and characterisation of two transiting planets observed by \textit{TESS} in the light curves of the young and bright (V=9.67) star HD73583 (TOI-560). We perform an intensive ...spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterise the system. We found that HD73583 is a young (\(\sim 500\)~Myr) active star with a rotational period of \(12.08 \pm 0.11 \)\,d, and a mass and radius of \( 0.73 \pm 0.02 M_\odot\) and \(0.65 \pm 0.02 R_\odot\), respectively. HD73583 b (\(P_b=6.3980420 _{ - 0.0000062 }^{+0.0000067}\) d) has a mass and radius of \(10.2 _{-3.1}^{+3.4} M_\oplus\) and\(2.79 \pm 0.10 R_\oplus\), respectively, that gives a density of \(2.58 _{-0.81}^{ 0.95} {\rm g\,cm^{-3}}\). HD73583 c (\(P_c= 18.87974 _{-0.00074 }^{+0.00086}\)) has a mass and radius of \(9.7_{-1.7} ^ {+1.8} M_\oplus\) and \(2.39_{-0.09}^{+0.10} R_\oplus\), respectively, this translates to a density of \(3.88 _{-0.80}^{+0.91} {\rm g\,cm^{-3}}\). Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect ongoing atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments.
