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Hi all, I observed the transient on Nov 1.887 with Lhires III and 150 l/mm grating (thank you François, Robin for the alert on other MLs). As reported by astronomers on BAAVSS, the spectrum is that of a normal star. The assumption for the brightening is now a microlensing event due to the gravitational field of an object moving in front of the distant star. The already known star normally shines at V mag ~14.1 but now increased at V ~11.5.



The profile, flux calibrated with V mag (simultaneous photometry):



The spectrum seems to be that of a white-yellow star reddened by interstellar dust. I tried to remove the extinction using the value E(B-V)=0.4 (not far from than as indicated by IRSA Dust service for the target coordinates). Just a test...

By comparing the dereddened profile with Pickles library profiles, I feel like I see a similarity with the intermediate F spectral class. In the following graph, the target spectrum is compared with Pickles F5V and F5III.



I don't know how long is an event like this. The raising steep phase began about 10 days ago (from the ASAS-SN light curve). Maybe there will be no spectra changes with time but I think it's interesting to know that there are such objects.

Paolo

Congratultaions for the reactivity and the anslysis, Paolo

François

This agrees with my ALPY 600 spectrum taken last night as already reported on spectro-l and the BAA forum (A significantly redenned main sequence F5v star)
https://www.britastro.org/comment/3856#comment-3856

We came to the same conclusion Paolo

Robin

Really nice work guys - well done. Very interesting indeed.

Paulo - could you elaborate on your before / after observations and differences with extinction values applied? I've not heard of or used the "IRSA Dust service" before. It might be a good discussion point (perhaps in a difference sub forum).

Paul

Hi Robin, Paul, thanks for your comments. I read the Robin message on Spectro-l with updates, very interesting. The lack of X-ray emission and the normal brightening in the UV (same amount of optical) confirm there is not an intrinsec variability but we are observing a microlensing event. The ASAS-SN light curve indicates that the fading phase is already started.

Paul, with regard to dust reddening I just fill the target coordinates to this service:
http://irsa.ipac.caltech.edu/applications/DUST/

It returns the Galaxy total amount of B-V reddening along the visual direction. It have some limitations, you can read here the details:
http://irsa.ipac.caltech.edu/applicatio ... round.html

Firstly, the extinction is related to all Galaxy dust for a line of sight. Indeed, E(B-V) is calculated using the colour of a number of elliptical galaxies. So I think we could consider it as a maximum value (the target might be found closer to us). Furthermore the resolution of extinction map does not take into account the fine structures in the interstellar medium.

For our target I initially used the returned E(B-V) value for the coordinates (0.5), then I start comparing the dereddened profile with the Pickles series exhibiting similar absorption lines. Found the spectral class that better matched the lines, I adjusted the value so that the continuum slope matched with the selected Pickles profile (~ 0.4).

I know that astronomers calculate the dust reddeding in a more rigorous manner on the basis of Na D doublet and a number of diffuse interstellar bands (DIB). However I think they need a good SNR and resolution that it’s difficult to find in amateur spectra.

Robin, the Alpy spectrum is fantastic! Perfect focus up to UV (mine start to blurry at H-delta). Really useful in case like this.

Sorry if I’m gone off topic here.
Clear sky!
Paolo

Paolo Berardi wrote: Robin, the Alpy spectrum is fantastic! Perfect focus up to UV (mine start to blurry at H-delta). Really useful in case like this.
Paolo

Thanks Paolo,

I do not often use my ALPY at full resolution with original 600 grism and I too was impressed at how far into the UV I could go. The work you do with the LHIRES shows how versatile it is but I do not enjoy using it in the UV, even at high resolution because the chromatic aberration is so bad there. It really deserves a better corrected lens, even just as an option.

Cheers
Robin

Hi Robin, I agree 100%, the Lhires III spectrograph need a more corrected doublet to enhance its versatility.

Sorry, a correction... I meant that here the spectrum blurring starts to be appreciable at H-gamma line (not at H-delta).

Paolo

A new ATel about the microlensing event, now on the decline:

ATEL #10926 ATEL #10926

Title: Follow-up Photometry of the Microlensing Event TCP J05074264+2447555
Author: R. Konyves-Toth, A. Pal, A. Ordasi, J. Vinko (Konkoly Observatory)
Queries: konyvestoth.reka@csfk.mta.hu
Posted: 5 Nov 2017; 01:24 UT
Subjects:Optical, Transient, Gravitational Lensing

We report photometric observations of TCP J05074264+2447555 (R.A. = 05:08:43,
Dec=+24:47:56), a proposed microlensing event at peak magnitude of V~11.5,
discovered by T.Kojima UT 2017-10-25.688,
and later confirmed by ASAS-SN (ATel #10923)

Our data were taken with the 60/90 cm Schmidt telescope and the 1-meter
RCC Telescope through Bessell B,V,R,I filters at Konkoly Observatory, Piszkesteto,
Hungary between UT 2017-11-03.9 and 2017-11-04.9.

Photometry was performed with IRAF/daophot by PSF-fitting using local
comparison stars for photometric reference. Standardized magnitudes were
tied to the PS1 photometry of the comparison
stars after transforming the PS1 gri magnitudes to the Johnson-Cousins
BVRI system.

We obtained the following magnitudes for TCP J05074264+2447555:

<big><big>
# MJD B eB V eV R eR I eI Instrument

58060.91 12.927 0.112 11.983 0.113 11.469 0.093 10.932 0.044 Schmidt

58060.99 12.973 0.137 12.054 0.083 11.575 0.086 10.994 0.037 Schmidt

58061.08 12.984 0.124 12.057 0.061 11.576 0.061 10.988 0.033 Schmidt

58061.12 12.905 0.116 12.100 0.045 11.549 0.052 10.992 0.060 Schmidt

58061.90 -- -- 12.164 0.026 11.659 0.029 11.125 0.022 1m_RCC
58061.94 13.057 0.114 12.233 0.063 11.742 0.059 11.160 0.054 Schmidt

</big></big>

These data confirm the prediction by Jayasinghe et al. (ATel #10923) that
the transient has been already passed maximum, and it is currently declining.
Our photometry is fully consistent with their predicted microlensing model
light curve.

Thank you François. May be interesting to take another spectrum when the brightness will be back to the normal state (we should not find abnormalities). Just to document a rare event with amateur equipment (as done by Robin with SA100 for the similar 2006 event in Cassiopea).

It's on the way (from Sky Patrol)...



Paolo

Hi all, so far it seems to me that little has changed in the spectrum, as predicted by the microlensing model. The star has not yet reached the previous state (~ V 14.1) but its brightness dropped to ~13.1 on Nov 11 (my last observation).



Fluxed spectra comparison in log intensity scale (some changes in the continuum).



The Nov 11 profile:



The ASAS-SN photometry with the microlensing model:



Paolo