possible gravitational microlensing event

[Robin Leadbeater]

If you get the chance tonight it would be worthwhile looking at the star in Taurus at

05 07 42.64 +24 47 55.5 J2000

(DSS field attached)

and perhaps taking a low resolution spectrum. 

Normally mag 15, it is currently brightening rapidly, possibly reaching a maximum of mag 9.  It is likely to be a rare gravitational microlensing event where an unseen object passes between us and the star. If this is the case, the spectrum should remain unchanged as the brightness returns to normal.

Here is the current light curve

https://asas-sn.osu.edu/light_curves/74d9ec6a-a023-48c5-b774-ad0a8449925a

 

Interestingly I observed a similar event in Cassiopeia in 2006, being lucky to record the earliest spectrum confirming it was probably not a normal variable star using Star Analyser

http://www.threehillsobservatory.co.uk/astro/spectra_30.htm

 

Cheers

Robin

Attachments:

1. 

   pos_grav_microlens.png
   

[David Swan]

Thanks for flagging this Robin. I can’t do spec, but I do have B, G and R CCD filters – so if the object is bright enough for my setup, I’ll take a set of images. David

[Nick White]

Thanks Robin, I spotted something at that position tonight (~23:00 UT Nov 1st) with averted vision through my 5” reflector. I watched for about an hour but didn’t notice any change in brightness (conditions improved as the night went on, making everything slightly easier to see by the time I packed up). 

[Nick James]

I’ve been following this star for the last few hours. It is a lot brighter than its catalogue mag (r=13.79) but doesn’t appear to be doing much.

[Nick James]

I’ve just got up and processed the rest of the frames. Here is the run through the night. The data gets noisy at the end as the sky brightens and the spike just before 0.7 is not real. It looks to be a cosmic ray hit on the CCD adjacent to the star.

[Robin Leadbeater]

Hi Nick, (and Nick)

Indeed.  I took a spectrum last night and thought similar eyeballing the guider image. Not the anticipated steepening climb.  David Boyd reported it steady at Vmag 11.50 last night so only slightly brighter than the last point on the ASAS-SN light curve. 

Robin 

[Robin Leadbeater]

Here is the spectrum (ALPY 600 at R~500) measured last night, shown  in blue. The features match those of an F star (F5v shown in red) but the continuum is significantly redder (smoothed ratio of measured/ Pickles f5v in green)

The full size version is in the attachment

Cheers

Robin

[Robin Leadbeater]

It looks like it has hit peak brightness and (barring any kicks from exoplanets) is now on its way back down

http://www.astronomy.ohio-state.edu/~assassin/followup/TCPJ05074264_2447555.pdf

http://www.astronomerstelegram.org/?read=10923

My  estimated F5v spectral classification is confirmed by a high resolution spectrum

http://www.astronomerstelegram.org/?read=10919

Cheers

Robin

[Nick James]

Nice work Robin.

[Nick White]

How common are microlensing events of this brightness? I had no idea such things could be observed visually with a small-ish telescope (I hope to follow it down using my 10″ telescope). Thanks all for sharing – ditto BAAVSS notices.

[Robin Leadbeater]

Hi Nick,

It is not something I follow but I think bright ones away from the galactic centre are very rare. (I remember the 2006 event in Cassiopeia was a big surprise to everyone).

There are  surveys looking for them in the galactic bulge which are followed up by amateurs through the MicroFun project

http://www.astronomy.ohio-state.edu/~microfun/

Cheers

Robin

[Robin Leadbeater]

Just seen this paper where they suggest that there was indeed a dip in the light curve around maximum indicating a “super earth” exoplanet

https://arxiv.org/abs/1802.06659

Robin

[Nick White]

Thanks Robin, spotted that paper. Looks like I missed the dip by half a day or so. Did anybody else here have luck with it?

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