(cba:news) Fwd: (cba:chat) some ASASSN-18ey = MAXI j1820-070 = "Maxie" chatter

Joe Patterson jp42 at columbia.edu
Wed May 30 07:51:20 EDT 2018 

Forwarded to cba-news just to cover the AU/NZ observers who could really 
help in this enterprise...

joe p



-------- Forwarded Message --------
Subject: 	(cba:chat) some ASASSN-18ey = MAXI j1820-070 = "Maxie" chatter
Date: 	Tue, 29 May 2018 12:08:42 -0400
From: 	Joe Patterson <jp42 at columbia.edu>
Reply-To: 	
To: 	



Hi CBAers,

I've more or less kept up with the impressive flow of CBA data on this
fascinating star.  The light curves are plenty noisy - all due to noise
in the STAR, not the measurement - but suggest a wave of period 0.328 d,
about twice that reported by Michael R. and Josch H.  It sometimes
appears as a double-hump wave, so it's tricky to tell them apart.  The
wave also may not be phase-stable, suggesting it might be a superhump
rather than the true orbital period.  Either is mighty welcome of
course, but especially the superhump since such things can reveal the
mass ratio - and thus possibly the black-hole mass.

These black-hole transients are RARE in our galaxy - I only know of ~8
in the last 40 years.  The noise (flickering, quasi-periods) in the
light curve is annoying, but this object will repay close study over the
next couple of months.

It would be great to get some data from AU/NZ.  The longish period
(assuming it's correct) creates some aliasing issues, and northern
Europe is substantially handicapped by the short nights.  Despite the
marginally northern dec, *southern* observers are in the best position
to get long runs.  Especially in Oceania, of course!

No disrespect for the other great star of the season, SDSS 1411+48,
which is flashing eclipses, rotation-period signals and a well-defined
dwarf-nova outburst.  I haven't yet gotten down and dirty with this
data, but it sure looks like fun.  The star has dipped to 17.5, but keep
watch on it; these stars can stage comebacks!


joe p



On 5/28/2018 3:39 PM, Josch Hambsch wrote:
>
> Hi Joe,
>
> I have been following 18ey every clear night since its discovery.
>
> Attached a screen shot from PERANSO showing most of the data (the gap 
> between about day 40 and 60 I still need to fill, data are available).
>
> As you can see there is a long term periodicity of about 37 days (the 
> one peak at about day 21 is due to observations in I and V band 
> filters, need to be removed). As well in the past two nights a 
> periodicity of about 0.16 days (about 3.8h) popped up as seen in the 
> colored data. Maybe this confirms what has been found by M. Richmond 
> in ATEL #11596.
>
> Regards,
>
> Josch
>
> *From:*cba-chat [mailto:cba-chat-bounces at cbastro.org] *On Behalf Of 
> *Stephen M. Brincat
> *Sent:* Freitag, 11. Mai 2018 10:28
> *To:* cba-chat at cbastro.org
> *Subject:* Re: (cba:chat) (cba:news) ASASSN-18ey = MAXI j1820-070
>
> Hi Joe,
>
> I regret that I will not be in a position to image for some days as I 
> am going through a mount upgrade. Weather can also be uncooperative 
> here as at this time of the year, humid conditions bring over low 
> altitude clouds that form over the mainland. This winter we had 
> persistent cloud cover with the remaining few clear nights coupled 
> with high winds.
>
> >> The most prolific observers so far are Michael Richmond in Rochester,
> NY, John Rock in England, Tonny Vanmunster in Belgium, and Stephen Brincat
> in Malta.  The first three are in famously cloudy and certainly northern
> locations, so their luck can't continue long.
>
> Regards & Clear Skies,
>
> Stephen
>
>
> /Flarestar Observatory
> IAU/MPC code: 171
> flarestar.weebly.com [ flarestar. weebly. com ] /
>
> On 10 May 2018 at 12:00, Joe Patterson <jop at astro.columbia.edu 
> <mailto:jop at astro.columbia.edu>> wrote:
>
> Hi CBAers,
>
> Some great data on this star rolling in.  It's declining VERY slowly - 
> still about V-12.8 - and showing some waves suggestive of a period 
> near 3.5 or 7 hours.  Promises to be a great target for the next month 
> or more.
>
> While a few runs showed some quasi-periodic oscillations with a 
> timescale near 12 s, this is a REALLY awkward timescale for us to 
> investigate.  The readout ("dead") time is a mighty big price to pay, 
> and I suggest we abandon this (high-speed) observing style.  We'll get 
> much better sensitivity if we adopt integration times appropriate for 
> the brightness - maybe 20 sec in clear light, or ~40 s in V (still 
> bright enough for V, if you like your V filter).
>
> The equatorial location and short northern nights are also somewhat 
> problematic, since we thrive on LONG nightly time series. We can 
> overcome this with an even-more-than-usually-extensive spread in 
> terrestrial longitude.  And let's do it!  This ia the brightest 
> black-hole transient in many years, and we already have a nice supply 
> of X-ray and Hubble data to accompany the optical time series.
>
> The most prolific observers so far are Michael Richmond in Rochester, 
> NY, John Rock in England, Tonny Vanmunster in Belgium, and Stephen 
> Brincat in Malta. The first three are in famously cloudy and certainly 
> northern locations, so their luck can't continue long.  There's not 
> much data yet from the western USA, so that would help a lot.  Also 
> AU/NZ, Africa, and southern Europe (except Brincat) have been quiet.
>
> Oops, I forgot Josch Hambsch from Chile.  His data, nearly every night 
> and well-calibrated, will eventually have a big impact.  But the lower 
> time resolution makes it less suitable for *defining* the features 
> (eclipses?) in the light curve.  So I hope that the USA observers will 
> keep a close watch on this fascinating star - which seems ready to 
> surrender a few secrets, but is making us work hard for them!
>
> joe p
>
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