Investigating the lack of main-sequence companions to massive Be stars

About 20% of all B-type stars are classical Be stars. The Be phenomenon is strongly correlated with rapid rotation, the origin of which remains unclear. It may be rooted in single- or binary-star evolution. In the framework of the binary channel, the initially more massive star transfers mass and angular momentum to the original secondary, which becomes a Be star. The system then evolves into a Be binary with a post-main-sequence companion, which may later be disrupted in a supernova event. Hence, if the binary channel dominates the formation of Be stars, one may expect a strong lack of close Be binaries with main sequence (MS) companions. Through an extensive, star-by-star review of the literature of a magnitude-limited sample of Galactic early-type Be stars, we investigate whether Be binaries with MS companions are known to exist. Our sample is constructed from the BeSS database and cross-matched with all available literature on the individual stars. Out of an initial list of 505 Be stars, we compile a final sample of 287 Galactic Be stars earlier than B1.5 with V<=12 mag. Out of those, 13 objects were reported as Be binaries with known post-MS companions and 11 as binaries with unknown, uncertain or debated companions. We find no confirmed reports of Be binaries with MS companions. For the remaining 263 targets, no significant reports of multiplicity exist in the literature, implying that they are either Be binaries with faint companions, or truly single. The clear lack of reported MS companions to Be stars, which stands in contrast to the high number of detected B+B MS binaries, strongly supports the hypothesis that early-type Be stars are binary interaction products that spun up after mass and angular momentum transfer from a companion star. Taken at face value, our results may suggest that a large majority of the early-type Be stars have formed through binary mass-transfer.Comment: 15 pages (incl. appendix), 6 figures, 3 tables, accepted for publication in A&

Farming today for young men and women

It would be impossible to list here all the advantages of farming. There are many. It is a life in the open, with a high degree of personal independence. There is opportunity to work closely as a family group. But if you’ve decided to farm because you’ve heard it’s an “ easy racket,” perhaps you’d better do some more thinking. Farming isn’t easy. Some years it’s tough. It’s a mistake to be misled by the war and immediate postwar picture. Conditions aren’t likely to stay this bright. We’re already hearing notes of warning about the price recessions— and even of depression. Prices undoubtedly will work downward after the present food emergency eases. Those of you who were raised on the farm know about the hard work. Those of you who weren’t should be aware of it. And you should know that the weather plays a mighty important part in your lives. Income is seasonal. Most farm homes are not as modern or as convenient as those in the city. Gay entertainment is not quite as close. If you are married, your wife, too, should be acquainted with the differences between farm and city living, because farming is a family affair

How to Grow Corn

A lot of things can make the difference between a good and poor corn crop. Some you can control - others you can\u27t. Here\u27s a roundup of present know-how about the factors you can\u27t control

MWC 656 is unlikely to contain a black hole

Context. MWC 656 was reported as the first known Be star with a black-hole (BH) companion in a 60 d period. The mass of the proposed BH companion is estimated to be between 4 - 7 MSun. This estimate is based on radial velocity (RV) measurements derived from the Fe ii 4583 emission line of the Be star disc and from the He ii 4686 emission line, assumed to be formed in a disc around the putative BH. Aims. Using new high-resolution spectroscopic data, we investigate whether MWC 656 truly contains a BH. Methods. We used the cross-correlation method to calculate the RVs of both the Be star and the He ii 4686 emission line and we derive a new orbital solution. We also performed disentangling to look for the spectral signature of a companion. Results. We derive an orbital period of 59.028 +- 0.011 d and a mass ratio q = M_Heii/M_Be = 0.12 +- 0.03, much lower than the previously reported q = 0.41 +- 0.07. Adopting a mass of the Be star of M_Be = 7.8 +- 2.0MSun, the companion has a mass of 0.94 +- 0.34MSun. For the upper limit of M_Be = 16MSun and q = 0.15, the companion has a mass 2.4MSun. Performing disentangling on mock spectra shows that the spectral signature of a non-degenerate stellar companion with such a low mass cannot be retrieved using our data. Conclusions. Our measurements do not support the presence of a BH companion in MWC 656. The derived upper limit on the mass of the companion rather indicates that it is a neutron star, a white dwarf, or a hot helium star. Far-UV data will help to reject or confirm a hot helium-star companion.Comment: 6 pages, 2 + 6 figures, 3 + 1 tables, accepted for publication in A&

Binary-object spectral-synthesis in 3D (BOSS-3D) -- Modelling H-alpha emission in the enigmatic multiple system LB-1

Context: To quantitatively decode the information stored within an observed spectrum, detailed modelling of the physical state and accurate radiative transfer solution schemes are required. In the analysis of stellar spectra, the numerical model often needs to account for binary companions and 3D structures in the stellar envelopes. The enigmatic binary (or multiple) system LB-1 constitutes a perfect example of such a complex multi-D problem. Aims: To improve our understanding of the LB-1 system, we directly modelled the phase-dependent H-alpha line profiles of this system. To this end, we developed a multi-purpose binary-object spectral-synthesis code in 3D (BOSS-3D). Methods: BOSS-3D calculates synthetic line profiles for a given state of the circumstellar material. The standard pz-geometry commonly used for single stars is extended by defining individual coordinate systems for each involved object and by accounting for the appropriate coordinate transformations. The code is then applied to the LB-1 system, considering two main hypotheses, a binary containing a stripped star and Be star, or a B star and a black hole with a disc. Results: Comparing these two scenarios, neither model can reproduce the detailed phase-dependent shape of the H-alpha line profiles. A satisfactory match with the observations, however, is obtained by invoking a disc around the primary object in addition to the Be-star disc or the black-hole accretion disc. Conclusions: The developed code can be used to model synthetic line profiles for a wide variety of binary systems, ranging from transit spectra of planetary atmospheres, to post-asymptotic giant branch binaries including circumstellar and circumbinary discs and massive-star binaries with stellar winds and disc systems. For the LB-1 system, our modelling provides strong evidence that each object in the system contains a disc-like structure

Searching for compact objects in the single-lined spectroscopic binaries of the young Galactic cluster NGC 6231

Recent evolutionary computations predict that a few percent of massive OB stars in binary systems should have a dormant BH companion. Despite several reported X-ray quiet OB+BH systems over the last couple of years, finding them with certainty remains challenging. These have great importance as they can be gravitational wave (GW) source progenitors, and are landmark systems in constraining supernova kick physics. This work aims to characterise the hidden companions to the single-lined spectroscopic binaries (SB1s) in the B star population of the young open Galactic cluster NGC 6231 to find candidate systems for harbouring compact object companions. With the orbital solutions for each SB1 previously constrained, we applied Fourier spectral disentangling to multi-epoch optical VLT/FLAMES spectra of each target to extract a potential signature of a faint companion, and to identify newly disentangled double-lined spectroscopic binaries (SB2s). For targets where the disentangling does not reveal any signature of a stellar companion, we performed atmospheric and evolutionary modelling on the primary to obtain constraints on the unseen companion. Seven newly classified SB2 systems with mass ratios down to near 0.1 were identified. From the remaining targets, for which no faint companion could be extracted from the spectra, four are found to have companion masses in the predicted mass ranges of neutron stars (NSes) and BHes. Two of these have companion masses between 1 and 3.5 $M_{\odot}$, making them potential hosts of NSes (or lower mass main sequence stars). The other two are between 2.5 to 8 $M_{\odot}$ and 1.6 and 26 $M_{\odot}$, respectively, and so are identified as candidates for harbouring BH companions. However, unambiguous identification of these systems as X-ray quiet compact object harbouring binaries requires follow up observations.Comment: Submitted to A&

Collective dynamics of liquid aluminum probed by Inelastic X-ray Scattering

An inelastic X-ray scattering experiment has been performed in liquid aluminum with the purpose of studying the collective excitations at wavevectors below the first sharp diffraction peak. The high instrumental resolution (up to 1.5 meV) allows an accurate investigation of the dynamical processes in this liquid metal on the basis of a generalized hydrodynamics framework. The outcoming results confirm the presence of a viscosity relaxation scenario ruled by a two timescale mechanism, as recently found in liquid lithium.Comment: 8 pages, 7 figure

Evidence of two viscous relaxation processes in the collective dynamics of liquid lithium

New inelastic X-ray scattering experiments have been performed on liquid lithium in a wide wavevector range. With respect to the previous measurements, the instrumental resolution, improved up to 1.5 meV, allows to accurately investigate the dynamical processes determining the observed shape of the the dynamic structure factor, $S(Q,\omega)$. A detailed analysis of the lineshapes shows the co-existence of relaxation processes with both a slow and a fast characteristic timescales, and therefore that pictures of the relaxation mechanisms based on a simple viscoelastic model must be abandoned.Comment: 5 pages, 4 .PS figure

Everything that glitters is not gold: V1315 Cas is not a dormant black hole

The quest for quiet or dormant black holes has been ongoing since several decades. Ellipsoidal variables possibly indicate the existence of a very high-mass invisible companion and are thought to be one of the best ways to find such dormant black holes. This, however, is not a panacea as we show here with one example. We indeed report the discovery of a new semi-detached interacting binary, V1315 Cas, discovered as an ellipsoidal variable. Using data from photometric surveys (ASAS-SN, TESS) and high-resolution spectroscopy, we derived a nearly circular orbit with an orbital period of $P_{\rm{orb}}$=34.54 d. The binary system consists of an evolved F-type star primary that is likely still filling its Roche lobe and a B-type star secondary. Using \textsc{phoebe}2, we derived the following masses and radii: for the primary, $M_p =0.84 \pm 0.03 \, M_\odot$ and $R_p =18.51^{+0.12}_{-0.07} \, R_\odot$; for the secondary, $M_s =7.3 \pm 0.3 \,M_\odot$ and $R_s =4.02^{+2.3}_{-2.0}\,R_\odot$. Modeling the evolution of the system with MESA, we found an age of $\sim$7.7e7 years. The system is at the end of a period of rapid non-conservative mass transfer that reversed its mass ratio, while significantly widening its orbit. The primary shows carbon depletion and nitrogen overabundance, indicative of CNO processed material being exposed due to mass transfer. An infrared excess as well as stationary H$\alpha$ emission suggest the presence of a circumstellar or circumbinary disc. V1315 Cas will likely become a detached stripped star binary.Comment: Accepted in MNRA