اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدBANYAN. VI. Discovery of a companion at the brown dwarf/planet-mass limit to a Tucana-Horologium M dwarf
134
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We report the discovery of a substellar companion to 2MASS J02192210-3925225, a young M6 $gamma$ candidate member of the Tucana-Horologium association (30 - 40 Myr). This L4 $gamma$ companion has been discovered with seeing-limited direct imaging observations; at a 4 separation (160AU) and a modest contrast ratio, it joins the very short list of young low-mass companions amenable to study without the aid of adaptive optics, enabling its characterization with a much wider suite of instruments than is possible for companions uncovered by high-contrast imaging surveys. With a model-dependent mass of 12-15MJup, it straddles the boundary between the planet and brown dwarf mass regimes. We present near-infrared spectroscopy of this companion and compare it to various similar objects uncovered in the last few years. The J0219-3925 system falls in a sparsely populated part of the host mass versus mass ratio diagram for binaries; the dearth of known similar companions may be due to observational biases in previous low-mass companion searches.
قيم البحث
اقرأ أيضاً
We report the discovery of an L dwarf companion to the A3V star beta{} Circini. VVV J151721.49-585131.5, or beta{} Cir B, was identified in a proper motion and parallax catalogue of the Vista Variables in the V{i}a L{a}ctea survey as having near infr
ared luminosity and colour indicative of an early L dwarf, and a proper motion and parallax consistent with that of beta{} Cir. The projected separation of $sim$3.6 corresponds to $6656$ au, which is unusually wide. The most recent published estimate of the age of the primary combined with our own estimate based on newer isochrones yields an age of $370-500$ Myr. The system therefore serves as a useful benchmark at an age greater than that of the Pleiades brown dwarfs and most other young L dwarf benchmarks. We have obtained a medium resolution echelle spectrum of the companion which indicates a spectral type of L1.0$pm$0.5 and lacks the typical signatures of low surface gravity seen in younger brown dwarfs. This suggests that signs of low surface gravity disappear from the spectra of early L dwarfs by an age of $sim370-500$ Myr, as expected from theoretical isochrones. The mass of beta{} Cir B is estimated from the BHAC15 isochrones as $0.056pm0.007$ M$_{odot}$.
We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010-03-18. This event was remarkable because the source was previously known to be photometrically v
ariable. Analyzing the pre-event source lightcurve, we demonstrate that it is an irregular variable over time scales >200d. Its dereddened color, $(V-I)_{S,0}$, is 1.221$pm$0.051mag and from our lens model we derive a source radius of 14.7$pm$1.3 $R_{odot}$, suggesting that it is a red giant star. We initially explored a number of purely microlensing models for the event but found a residual gradient in the data taken prior to and after the event. This is likely to be due to the variability of the source rather than part of the lensing event, so we incorporated a slope parameter in our model in order to derive the true parameters of the lensing system. We find that the lensing system has a mass ratio of q=0.0654$pm$0.0006. The Einstein crossing time of the event, $T_{rm{E}}=44.3$pm$0.1d, was sufficiently long that the lightcurve exhibited parallax effects. In addition, the source trajectory relative to the large caustic structure allowed the orbital motion of the lens system to be detected. Combining the parallax with the Einstein radius, we were able to derive the distance to the lens, $D_L$=2.8$pm$0.4kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with $M_{L,p}$=0.16$pm0.03M_{odot}$ while the companion has $M_{L,s}$=11.0$pm2.0M_{rm{J}}$ putting it in the boundary zone between planets and brown dwarfs.
We present the discovery of CWISE J203546.35-493611.0, a peculiar M8 companion to the M4.5 star APMPM J2036-4936 discovered through the citizen science project Backyard Worlds: Planet 9. Given CWISE J203546.35-493611.0s proper motion ($mu_{alpha}$, $
mu_{delta}$) = ($-$126$pm$22, $-$478$pm$23) and angular separation of 34.2$$ from APMPM 2036-4936, we calculate a chance alignment probability of $1.15 times 10^{-6}$. Both stars in this system appear to be underluminous, and the spectrum obtained for CWISE J203546.35-493611.0 shows a triangular H band. Further study of this system is warranted to understand these peculiarities.
We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT/SPHERE during the SHINE exoplanet survey. The host is a B9.5V member of the Lower-Centaurus-Crux subgroup of the Scorpius Centaurus OB association. The
measured angular separation of the companion ($1.2705pm0.0023$) corresponds to a projected distance of $159pm12$ AU. We observed the target with the dual-band imaging and long-slit spectroscopy modes of the IRDIS imager to obtain its SED and astrometry. In addition, we reprocessed archival NACO L-band data, from which we also recover the companion. Its SED is consistent with a young (<30 Myr), low surface gravity object with a spectral type of M9$_{gamma}pm1$. From comparison with the BT-Settl atmospheric models we estimate an effective temperature of $T_{textrm{eff}}=2600 pm 100$ K, and comparison of the companion photometry to the COND evolutionary models yields a mass of $sim29-37$ M$_{text{J}}$ at the estimated age of $16^{+15}_{-7}$ Myr for the system. HIP 64892 is a rare example of an extreme-mass ratio system ($qsim0.01$) and will be useful for testing models relating to the formation and evolution of such low-mass objects.
We analyze KMT-2019-BLG-1339, a microlensing event with an obvious but incompletely resolved brief anomaly feature around the peak of the light curve. Although the origin of the anomaly is identified to be a companion to the lens with a low mass rati
o $q$, the interpretation is subject to two different degeneracy types. The first type is the ambiguity in $rho$, representing the angular source radius scaled to the angular radius of the Einstein ring, $theta_{rm E}$, and the other is the $sleftrightarrow s^{-1}$ degeneracy. The former type, `finite-source degeneracy, causes ambiguities in both $s$ and $q$, while the latter induces an ambiguity only in $s$. Here $s$ denotes the separation (in units of $theta_{rm E}$) in projection between the lens components. We estimate that the lens components have masses $(M_1, M_2)sim (0.27^{+0.36}_{-0.15}~M_odot, 11^{+16}_{-7}~M_{rm J})$ and $sim (0.48^{+0.40}_{-0.28}~M_odot, 1.3^{+1.1}_{-0.7}~M_{rm J})$ according to the two solutions subject to the finite-source degeneracy, indicating that the lens comprises an M dwarf and a companion with a mass around the planet/brown dwarf boundary or a Jovian-mass planet. It is possible to lift the finite-source degeneracy by conducting future observations utilizing a high resolution instrument because the relative lens-source proper motion predicted by the solutions are widely different.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
